The auth_password function in auth-passwd.c in sshd in OpenSSH before 7.3 does not limit password lengths for password authentication, which allows remote attackers to cause a denial of service (crypt CPU consumption) via a long string.

The version of Junos OS installed on the remote host is prior to 12.3X48-D55, 12.3R12-S13, 15.1X49-D100, 15.1F6-S12, 16.1R3-S4, 16.2R1-S4, 17.1R1-S2, or 17.2R1. It is, therefore, affected by a vulnerability as referenced in the JSA10940 advisory. Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

There is no limit on the password length. Impact : A remote attacker may be able to cause an affected SSH server to use excessive amount of CPU by sending very long passwords, when PasswordAuthentication is enabled by the system administrator.

A covert timing channel flaw was found in the way OpenSSH handled authentication of non-existent users. A remote unauthenticated attacker could possibly use this flaw to determine valid user names by measuring the timing of server responses. (CVE-2016-6210)

It was found that OpenSSH did not limit password lengths for password authentication. A remote unauthenticated attacker could use this flaw to temporarily trigger high CPU consumption in sshd by sending long passwords. (CVE-2016-6515)

It was found that ssh-agent could load PKCS#11 modules from arbitrary paths. An attacker having control of the forwarded agent-socket on the server, and the ability to write to the filesystem of the client host, could use this flaw to execute arbitrary code with the privileges of the user running ssh-agent. (CVE-2016-10009)

It was found that the host private key material could possibly leak to the privilege-separated child processes via re-allocated memory. An attacker able to compromise the privilege-separated process could therefore obtain the leaked key information. (CVE-2016-10011)

It was found that the boundary checks in the code implementing support for pre-authentication compression could have been optimized out by certain compilers. An attacker able to compromise the privilege-separated process could possibly use this flaw for further attacks against the privileged monitor process. (CVE-2016-10012)

The version of the FreeBSD kernel running on the remote host is prior to 10.3-RELEASE-p21, 11.0 prior to 11.0-RELEASE-p12, or 11.1 prior to 11.1-RELEASE-p1. It, therefore, affected by a flaw in built-in password authentication in OpenSSH. An unauthenticated, remote attacker can exploit this issue by sending very long passwords when PasswordAuthentication is enabled by the system administrator, resulting in a denial of service condition.

Note that this issue only affects hosts with PasswordAuthentication enabled in /etc/ssh/sshd_config (the default FreeBSD configuration).

You may workaround this issue by disabling PasswordAuthentication and restarting sshd.

An update for openssh is now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having a security impact of Moderate. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

The following packages have been upgraded to a later upstream version:
openssh (7.4p1). (BZ#1341754)

Security Fix(es) :

* A covert timing channel flaw was found in the way OpenSSH handled authentication of non-existent users. A remote unauthenticated attacker could possibly use this flaw to determine valid user names by measuring the timing of server responses. (CVE-2016-6210)

* It was found that OpenSSH did not limit password lengths for password authentication. A remote unauthenticated attacker could use this flaw to temporarily trigger high CPU consumption in sshd by sending long passwords. (CVE-2016-6515)

* It was found that ssh-agent could load PKCS#11 modules from arbitrary paths. An attacker having control of the forwarded agent-socket on the server, and the ability to write to the filesystem of the client host, could use this flaw to execute arbitrary code with the privileges of the user running ssh-agent. (CVE-2016-10009)

* It was found that the host private key material could possibly leak to the privilege-separated child processes via re-allocated memory. An attacker able to compromise the privilege-separated process could therefore obtain the leaked key information. (CVE-2016-10011)

* It was found that the boundary checks in the code implementing support for pre-authentication compression could have been optimized out by certain compilers. An attacker able to compromise the privilege-separated process could possibly use this flaw for further attacks against the privileged monitor process. (CVE-2016-10012)

Additional Changes :

For detailed information on changes in this release, see the Red Hat Enterprise Linux 7.4 Release Notes linked from the References section.

The following packages have been upgraded to a later upstream version:
openssh (7.4p1).

Security Fix(es) :

  - A covert timing channel flaw was found in the way     OpenSSH handled authentication of non-existent users. A     remote unauthenticated attacker could possibly use this     flaw to determine valid user names by measuring the     timing of server responses. (CVE-2016-6210)

  - It was found that OpenSSH did not limit password lengths     for password authentication. A remote unauthenticated     attacker could use this flaw to temporarily trigger high     CPU consumption in sshd by sending long passwords.
    (CVE-2016-6515)

  - It was found that ssh-agent could load PKCS#11 modules     from arbitrary paths. An attacker having control of the     forwarded agent-socket on the server, and the ability to     write to the filesystem of the client host, could use     this flaw to execute arbitrary code with the privileges     of the user running ssh-agent. (CVE-2016-10009)

  - It was found that the host private key material could     possibly leak to the privilege-separated child processes     via re-allocated memory. An attacker able to compromise     the privilege-separated process could therefore obtain     the leaked key information. (CVE-2016-10011)

  - It was found that the boundary checks in the code     implementing support for pre-authentication compression     could have been optimized out by certain compilers. An     attacker able to compromise the privilege-separated     process could possibly use this flaw for further attacks     against the privileged monitor process. (CVE-2016-10012)

From Red Hat Security Advisory 2017:2029 :

An update for openssh is now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having a security impact of Moderate. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating systems. It includes the core files necessary for both the OpenSSH client and server.

The following packages have been upgraded to a later upstream version:
openssh (7.4p1). (BZ#1341754)

Security Fix(es) :

* A covert timing channel flaw was found in the way OpenSSH handled authentication of non-existent users. A remote unauthenticated attacker could possibly use this flaw to determine valid user names by measuring the timing of server responses. (CVE-2016-6210)

* It was found that OpenSSH did not limit password lengths for password authentication. A remote unauthenticated attacker could use this flaw to temporarily trigger high CPU consumption in sshd by sending long passwords. (CVE-2016-6515)

* It was found that ssh-agent could load PKCS#11 modules from arbitrary paths. An attacker having control of the forwarded agent-socket on the server, and the ability to write to the filesystem of the client host, could use this flaw to execute arbitrary code with the privileges of the user running ssh-agent. (CVE-2016-10009)

* It was found that the host private key material could possibly leak to the privilege-separated child processes via re-allocated memory. An attacker able to compromise the privilege-separated process could therefore obtain the leaked key information. (CVE-2016-10011)

* It was found that the boundary checks in the code implementing support for pre-authentication compression could have been optimized out by certain compilers. An attacker able to compromise the privilege-separated process could possibly use this flaw for further attacks against the privileged monitor process. (CVE-2016-10012)

Additional Changes :

For detailed information on changes in this release, see the Red Hat Enterprise Linux 7.4 Release Notes linked from the References section.

The remote AIX host has a version of OpenSSH installed that is affected by the following vulnerabilities :

  - An elevation of privilege vulnerability exists in the     do_setup_env() function within file session.c when     handling user-supplied environmental variables. A local     attacker can exploit this to gain elevated privileges by     triggering a crafted environment for the /bin/login     program. This vulnerability requires that the UseLogin     feature is enabled and that PAM is configured to read     .pam_environment files in user home directories.
    (CVE-2015-8325)

  - A flaw exists when handling authentication requests that     involve overly long passwords due to returning shorter     response times for requests for invalid users than for     valid users. An unauthenticated, remote attacker can     exploit this to enumerate valid usernames by conducting     a timing attack. (CVE-2016-6210)

  - A denial of service vulnerability exists in the     auth_password() function within auth-passwd.c due to a     a failure to limit password lengths. An unauthenticated,     remote attacker can exploit this, via overly long     passwords, to cause the excessive consumption of CPU     resources. (CVE-2016-6515)

The auth_password function in auth-passwd.c in sshd in OpenSSH before 7.3 does not limit password lengths for password authentication, which allows remote attackers to cause a denial of service (crypt CPU consumption) via a long string. (CVE-2016-6515)

This update for OpenSSH fixes the following issues :

  - Prevent user enumeration through the timing of password     processing. (bsc#989363, CVE-2016-6210)

  - Allow lowering the DH groups parameter limit in server     as well as when GSSAPI key exchange is used.
    (bsc#948902)

  - Sanitize input for xauth(1). (bsc#970632, CVE-2016-3115)

  - Prevent X11 SECURITY circumvention when forwarding X11     connections. (bsc#962313, CVE-2016-1908)

  - Disable DH parameters under 2048 bits by default and     allow lowering the limit back to the RFC 4419 specified     minimum through an option. (bsc#932483, bsc#948902)

  - Ignore PAM environment when using login. (bsc#975865,     CVE-2015-8325)

  - Limit the accepted password length (prevents a possible     denial of service). (bsc#992533, CVE-2016-6515)

  - Relax version requires for the openssh-askpass     sub-package. (bsc#962794)

  - Avoid complaining about unset DISPLAY variable.
    (bsc#981654)

  - Initialize message id to prevent connection breakups in     some cases. (bsc#959096)

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

This update for openssh fixes the following issues :

  - Prevent user enumeration through the timing of password     processing (bsc#989363, CVE-2016-6210)

  - Allow lowering the DH groups parameter limit in server     as well as when GSSAPI key exchange is used (bsc#948902)

  - limit accepted password length (prevents possible DoS)     (bsc#992533, CVE-2016-6515)

Bug fixes :

  - avoid complaining about unset DISPLAY variable     (bsc#981654)

This update was imported from the SUSE:SLE-12:Update update project.

This update for openssh fixes the following issues :

  - CVE-2016-6210: Prevent user enumeration through the     timing of password processing (bsc#989363)     [-prevent_timing_user_enumeration]

  - Allow lowering the DH groups parameter limit in server     as well as when GSSAPI key exchange is used (bsc#948902)

  - CVE-2016-6515: Limiting the accepted password length to     prevent possible DoS (bsc#992533) Bug fixes :

  - avoid complaining about unset DISPLAY variable     (bsc#981654)

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

This update for openssh fixes the following issues :

  - Prevent user enumeration through the timing of password     processing (bsc#989363, CVE-2016-6210)     [-prevent_timing_user_enumeration]

  - Allow lowering the DH groups parameter limit in server     as well as when GSSAPI key exchange is used (bsc#948902)

  - limit accepted password length (prevents possible DoS)     (bsc#992533, CVE-2016-6515) Bug fixes :

  - avoid complaining about unset DISPLAY variable     (bsc#981654)

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

According to its banner, the version of OpenSSH running on the remote host is prior to 7.3. It is, therefore, affected by multiple vulnerabilities :

  - A local privilege escalation when the UseLogin feature     is enabled and PAM is configured to read .pam_environment     files from home directories. (CVE-2015-8325)

  - A flaw exists that is due to the program returning     shorter response times for authentication requests with     overly long passwords for invalid users than for valid     users. This may allow a remote attacker to conduct a     timing attack and enumerate valid usernames.
    (CVE-2016-6210)

  - A denial of service vulnerability exists in the     auth_password() function in auth-passwd.c due to a     failure to limit password lengths for password     authentication. An unauthenticated, remote attacker can     exploit this, via a long string, to consume excessive     CPU resources, resulting in a denial of service     condition. (CVE-2016-6515)

  - An unspecified flaw exists in the CBC padding oracle     countermeasures that allows an unauthenticated, remote     attacker to conduct a timing attack.

  - A flaw exists due to improper operation ordering of MAC     verification for Encrypt-then-MAC (EtM) mode transport     MAC algorithms when verifying the MAC before decrypting     any ciphertext. An unauthenticated, remote attacker can     exploit this, via a timing attack, to disclose sensitive     information.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Eddie Harari discovered that OpenSSH incorrectly handled password hashing when authenticating non-existing users. A remote attacker could perform a timing attack and enumerate valid users.
(CVE-2016-6210)

Tomas Kuthan, Andres Rojas, and Javier Nieto discovered that OpenSSH did not limit password lengths. A remote attacker could use this issue to cause OpenSSH to consume resources, leading to a denial of service.
(CVE-2016-6515).

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

OpenSSH secure shell client and server had a denial of service vulnerability reported.

CVE-2016-6515 The password authentication function in sshd in OpenSSH before 7.3 does not limit password lengths for password authentication, which allows remote attackers to cause a denial of service (crypt CPU consumption) via a long string.

For Debian 7 'Wheezy', this problems has been fixed in version 6.0p1-4+deb7u6.

We recommend that you upgrade your openssh packages.

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

The current version of OpenSSH is 7.x prior to 7.3 and is affected by the following vulnerabilities :

 - A flaw in the 'do_setup_env()' function in 'session.c' is triggered when handling user-supplied environmental variables. This may potentially allow a local attacker to gain elevated privileges.
 - A flaw exists due to the program returning shorter response times for authentication requests with overly long passwords for invalid users than for valid users. This may allow a remote attacker to conduct a timing attack and enumerate valid usernames.
 - A flaw in the 'crypt(3)' function via 'sshd(8)' is triggered during the handling of overly long passwords. This may allow a remote attacker to consume excessive CPU resources.
 - An unspecified flaw in the 'CBC' padding oracle countermeasures in 'ssh(1)' and 'sshd(8)', which may allow an attacker to conduct a timing attack. No further details have been provided.
 - A flaw in 'ssh(1)' and 'sshd(8)' is due to improper operation ordering of MAC verification for Encrypt-then-MAC (EtM) mode transport MAC algorithms to verify the MAC before decrypting any ciphertext. This may allow a remote attacker to use a timing attack to gain unauthorized access to potentially sensitive information.
 - A flaw exists in the 'crypt(3)' function, accessed via 'sshd(8)', that is triggered during the handling of overly long passwords.  This may allow a remote attacker to affect the consumption of CPU resources.
 - An unspecified timing flaw exists in the CBC padding oracle countermeasures in the 'ssh(1)' and 'sshd(8)' functions.  This may allow a remote attacker to gain access to potentially sensitive information.

Security fix for CVE-2016-6515

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website.
Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

ID	Name	Product	Family	Severity
130514	Juniper JSA10940	Nessus	Junos Local Security Checks	high
103657	FreeBSD : FreeBSD -- OpenSSH Denial of Service vulnerability (6ed5c5e3-a840-11e7-b5af-a4badb2f4699)	Nessus	FreeBSD Local Security Checks	high
103650	Amazon Linux AMI : openssh (ALAS-2017-898)	Nessus	Amazon Linux Local Security Checks	high
102917	FreeBSD < 10.3-RELEASE-p21 / 11.0 < 11.0-RELEASE-p12 / 11.1 < 11.1-RELEASE-p1 OpenSSH Password Length DoS (FreeBSD-SA-17:06.openssh)	Nessus	FreeBSD Local Security Checks	high
102751	CentOS 7 : openssh (CESA-2017:2029)	Nessus	CentOS Local Security Checks	high
102650	Scientific Linux Security Update : openssh on SL7.x x86_64 (20170801)	Nessus	Scientific Linux Local Security Checks	high
102296	Oracle Linux 7 : openssh (ELSA-2017-2029)	Nessus	Oracle Linux Local Security Checks	high
102112	RHEL 7 : openssh (RHSA-2017:2029)	Nessus	Red Hat Local Security Checks	high
95477	AIX OpenSSH Advisory : openssh_advisory9.asc	Nessus	AIX Local Security Checks	high
94147	F5 Networks BIG-IP : OpenSSH vulnerability (K31510510)	Nessus	F5 Networks Local Security Checks	high
93735	SUSE SLES11 Security Update : openssh (SUSE-SU-2016:2388-1)	Nessus	SuSE Local Security Checks	critical
93598	openSUSE Security Update : openssh (openSUSE-2016-1096)	Nessus	SuSE Local Security Checks	high
93456	SUSE SLES11 Security Update : openssh (SUSE-SU-2016:2281-1)	Nessus	SuSE Local Security Checks	high
93455	SUSE SLED12 / SLES12 Security Update : openssh (SUSE-SU-2016:2280-1)	Nessus	SuSE Local Security Checks	high
93194	OpenSSH < 7.3 Multiple Vulnerabilities	Nessus	Misc.	high
92985	Ubuntu 14.04 LTS / 16.04 LTS : OpenSSH vulnerabilities (USN-3061-1)	Nessus	Ubuntu Local Security Checks	medium
92953	Debian DLA-594-1 : openssh security update	Nessus	Debian Local Security Checks	high
9507	OpenSSH 7.x < 7.3 Multiple Vulnerabilities	Nessus Network Monitor	SSH	high
92849	Fedora 24 : openssh (2016-4a3debc3a6)	Nessus	Fedora Local Security Checks	high

Detections

Analytics

CVE-2016-6515

high

Tenable Plugins

high

high

high

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high

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high

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critical

high

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medium

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