Several vulnerabilities have been discovered in the Linux kernel that may lead to the execution of arbitrary code, privilege escalation, denial of service, or information leaks.

CVE-2020-24586, CVE-2020-24587, CVE-2020-26147

Mathy Vanhoef discovered that many Wi-Fi implementations, including Linux's mac80211, did not correctly implement reassembly of fragmented packets. In some circumstances, an attacker within range of a network could exploit these flaws to forge arbitrary packets and/or to access sensitive data on that network.

CVE-2020-24588

Mathy Vanhoef discovered that most Wi-Fi implementations, including Linux's mac80211, did not authenticate the 'is aggregated' packet header flag. An attacker within range of a network could exploit this to forge arbitrary packets on that network.

CVE-2020-25670, CVE-2020-25671, CVE-2021-23134

kiyin (&#x5C39;&#x4EAE;) of TenCent discovered several reference counting bugs in the NFC LLCP implementation which could lead to use-after-free. A local user could exploit these for denial of service (crash or memory corruption) or possibly for privilege escalation.

Nadav Markus and Or Cohen of Palo Alto Networks discovered that the original fixes for these introduced a new bug that could result in use-after-free and double-free. This has also been fixed.

CVE-2020-25672

kiyin (&#x5C39;&#x4EAE;) of TenCent discovered a memory leak in the NFC LLCP implementation. A local user could exploit this for denial of service (memory exhaustion).

CVE-2020-26139

Mathy Vanhoef discovered that a bug in some Wi-Fi implementations, including Linux's mac80211. When operating in AP mode, they would forward EAPOL frames from one client to another while the sender was not yet authenticated. An attacker within range of a network could use this for denial of service or as an aid to exploiting other vulnerabilities.

CVE-2020-26558, CVE-2021-0129

Researchers at ANSSI discovered vulnerabilities in the Bluetooth Passkey authentication method, and in Linux's implementation of it. An attacker within range of two Bluetooth devices while they pair using Passkey authentication could exploit this to obtain the shared secret (Passkey) and then impersonate either of the devices to each other.

CVE-2020-29374

Jann Horn of Google reported a flaw in Linux's virtual memory management. A parent and child process initially share all their memory, but when either writes to a shared page, the page is duplicated and unshared (copy-on-write). However, in case an operation such as vmsplice() required the kernel to take an additional reference to a shared page, and a copy-on-write occurs during this operation, the kernel might have accessed the wrong process's memory. For some programs, this could lead to an information leak or data corruption.

CVE-2021-3483

&#x9A6C;&#x54F2;&#x5B87; (Zheyu Ma) reported a bug in the 'nosy' driver for TI PCILynx FireWire controllers, which could lead to list corruption and a use-after-free. On a system that uses this driver, local users granted access to /dev/nosy could exploit this to cause a denial of service (crash or memory corruption) or possibly for privilege escalation.

CVE-2021-3506

The ADLab of venustech discovered a bug in the F2FS driver which could lead to an out-of-bounds read when accessing a crafted filesystem. A local user permitted to mount arbitrary filesystems could exploit this to cause a denial of service (crash) or other security impact.

CVE-2021-3564, CVE-2021-3573, CVE-2021-32399

The BlockSec team discovered several race conditions in the Bluetooth subsystem that could lead to a use-after-free or double-free. A local user could exploit these to caue a denial of service (crash or memory corruption) or possibly for privilege escalation.

CVE-2021-3587

Active Defense Lab of Venustech discovered a potential NULL pointer dereference in the NFC LLCP implementation. A local user could use this to cause a denial of service (crash).

CVE-2021-23133

Or Cohen of Palo Alto Networks discovered a race condition in the SCTP implementation, which can lead to list corruption. A local user could exploit this to cause a denial of service (crash or memory corruption) or possibly for privilege escalation.

CVE-2021-28688 (XSA-371)

It was discovered that the original fix for CVE-2021-26930 (XSA-365) introduced a potential resource leak. A malicious guest could presumably exploit this to cause a denial of service (resource exhaustion) within the host.

CVE-2021-28964

Zygo Blaxell reported a race condition in the Btrfs driver which can lead to an assertion failure. On systems using Btrfs, a local user could exploit this to cause a denial of service (crash).

CVE-2021-28971

Vince Weaver reported a bug in the performance event handler for Intel PEBS. A workaround for a hardware bug on Intel CPUs codenamed 'Haswell' and earlier could lead to a NULL pointer dereference. On systems with the affected CPUs, if users are permitted to access performance events, a local user may exploit this to cause a denial of service (crash).

By default, unprivileged users do not have access to performance events, which mitigates this issue. This is controlled by the kernel.perf_event_paranoid sysctl.

CVE-2021-29154

It was discovered that the Extended BPF (eBPF) JIT compiler for x86_64 generated incorrect branch instructions in some cases. On systems where eBPF JIT is enabled, users could exploit this to execute arbitrary code in the kernel.

By default, eBPF JIT is disabled, mitigating this issue.
This is controlled by the net.core.bpf_jit_enable sysctl.

CVE-2021-29155, CVE-2021-31829

Piotr Krysiuk and Benedict Schlueter discovered that the Extended BPF (eBPF) verifier did not completely protect against information leaks due to speculative execution. A local user could exploit these to obtain sensitive information from kernel memory.

CVE-2021-29264

It was discovered that the 'gianfar' Ethernet driver used with some Freescale SoCs did not correctly handle a Rx queue overrun when jumbo packets were enabled. On systems using this driver and jumbo packets, an attacker on the network could exploit this to cause a denial of service (crash).

This driver is not enabled in Debian's official kernel configurations.

CVE-2021-29647

The syzbot tool found an information leak in the Qualcomm IPC Router (qrtr) implementation.

This protocol is not enabled in Debian's official kernel configurations.

CVE-2021-29650

It was discovered that a data race in the netfilter subsystem could lead to a NULL pointer dereference during replacement of a table. A local user with CAP_NET_ADMIN capability in any user namespace could use this to cause a denial of service (crash).

By default, unprivileged users cannot create user namespaces, which mitigates this issue. This is controlled by the kernel.unprivileged_userns_clone sysctl.

CVE-2021-31916

Dan Carpenter reported incorrect parameter validation in the device-mapper (dm) subsystem, which could lead to a heap buffer overrun. However, only users with CAP_SYS_ADMIN capability (i.e.
root-equivalent) could trigger this bug, so it did not have any security impact in this kernel version.

CVE-2021-33034

The syzbot tool found a bug in the Bluetooth subsystem that could lead to a use-after-free. A local user could use this to cause a denial of service (crash or memory corruption) or possibly for privilege escalation.

For Debian 9 stretch, these problems have been fixed in version 4.19.194-1~deb9u1. This update additionally fixes Debian bug #986949, #988352, and #989451; and includes many more bug fixes from stable updates 4.19.182-4.19.194 inclusive.

We recommend that you upgrade your linux-4.19 packages.

For the detailed security status of linux-4.19 please refer to its security tracker page at:
https://security-tracker.debian.org/tracker/linux-4.19

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.

New kernel packages are available for Slackware 14.2 to fix a security issue.

ID	Name	Product	Family	Published	Updated	Severity
150984	Debian DLA-2690-1 : linux-4.19 security update	Nessus	Debian Local Security Checks	6/24/2021	1/16/2024	high
151897	Slackware 14.2 : Slackware 14.2 kernel (SSA:2021-202-01)	Nessus	Slackware Local Security Checks	7/21/2021	10/6/2025	high

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