Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

The remote Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 25.10 host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8182-1 advisory.

    Andrew Lacambra discovered that Rack did not properly parse certain regular expressions. An attacker could     possibly use this issue to bypass network security filters. This issue only affected Ubuntu 20.04 LTS,     Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. (CVE-2026-26961)

    William T. Nelson discovered that Rack did not handle multipart headers correctly. An attacker could     possibly use this issue to cause downstream parsing issues or a denial of service. This issue only     affected Ubuntu 25.10. (CVE-2026-26962)

    It was discovered that Rack did not handle the Forwarded header correctly. An attacker could possibly use     this issue to manipulate header values. This issue only affected Ubuntu 25.10. (CVE-2026-32762)

    It was discovered that Rack could consume excessive CPU when handling certain Accept-Encoding values. An     attacker could possibly use this issue to cause a denial of service. (CVE-2026-34230)

    Haruki Oyama discovered that certain configurations of Rack could erroneously fail to derive the displayed     directory path, and expose the full filesystem path. An attacker could possibly use this issue to disclose     deployment details such as layout and usernames. (CVE-2026-34763)

    It was discovered that Rack did not properly handle static file paths. An attacker could possibly use this     issue to exfiltrate unintentionally served data. (CVE-2026-34785)

    Haruki Oyama discovered that Rack did not apply header rules to certain requests for URL-encoded static     paths. An attacker could possibly use this issue to bypass security-relevant response headers. This issue     only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10.
    (CVE-2026-34786)

    It was discovered that Rack did not limit the number of ranges requested in the Range header. An attacker     could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 16.04 LTS,     Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. (CVE-2026-34826)

    It was discovered that Rack could consume excessive CPU when parsing certain multipart parameters. An     attacker could possibly use this to cause a denial of service. This issue only affected Ubuntu 25.10.
    (CVE-2026-34827)

    It was discovered that Rack could consume unbounded disk space when handling requests without a Content-     Length header. An attacker could possibly use this issue to cause a denial of service. This issue only     affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. (CVE-2026-34829)

    Mehtab Zafar discovered that Rack directly interpreted the X-Accel-Mapping header as a regular expression     without escaping. An attacker could possibly use this issue to exfiltrate arbitrary files from internal     locations. This issue only affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04     LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. (CVE-2026-34830)

    It was discovered that Rack did not properly handle messages with Unicode. An attacker could possibly use     this issue to cause a denial of service. This issue only affected Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and     Ubuntu 25.10. (CVE-2026-34831)

    It was discovered that Rack did not properly parse the Host header. An attacker could possibly use this     issue to bypass security filters or poison generated links. This issue only affected Ubuntu 25.10.
    (CVE-2026-34835)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

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

The version of the Rack Ruby library installed on the remote host is prior to 2.2.23, prior to 3.1.21, or prior to 3.2.6.
It is, therefore, affected by multiple vulnerabilities:

  - Rack::Utils.get_byte_ranges parses HTTP Range header without limiting the number of individual byte ranges,     leading to denial of service (CVE-2026-34826)

  - Rack::Static uses simple string prefix check allowing unintended file disclosure (CVE-2026-34785)

  - Rack::Utils.select_best_encoding has quadratic time complexity with many wildcard Accept-Encoding     entries (CVE-2026-34230)

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

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6,     Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a     regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not     escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and     control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-     redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal     locations. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6. (CVE-2026-34830)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
307009	Ubuntu 14.04 LTS / 16.04 LTS / 18.04 LTS / 20.04 LTS / 22.04 LTS / 24.04 LTS / 25.10 : Rack vulnerabilities (USN-8182-1)	Nessus	Ubuntu Local Security Checks	high
305959	Ruby Rack < 2.2.23 / 3.0.x < 3.1.21 / 3.2 < 3.2.6 Multiple Vulnerabilities	Nessus	Misc.	high
304836	Linux Distros Unpatched Vulnerability : CVE-2026-34830	Nessus	Misc.	high

Detections

Analytics

CVE-2026-34830

high

Tenable Plugins

high

high

high