Rack is a modular Ruby web server interface. From version 3.2.0 to before version 3.2.6, Rack::Multipart::Parser unfolds folded multipart part headers incorrectly. When a multipart header contains an obs-fold sequence, Rack preserves the embedded CRLF in parsed parameter values such as filename or name instead of removing the folded line break during unfolding. As a result, applications that later reuse those parsed values in HTTP response headers may be vulnerable to downstream header injection or response splitting. This issue has been patched in version 3.2.6.

The remote SUSE Linux SLES15 / SLES_SAP15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:1745-1 advisory.

    Update to version 2.27.

    Security issues fixed:

    - CVE-2026-26961: rack: greedy multipart boundary parsing can lead to parser differentials and WAF bypass       (bsc#1261398).
    - CVE-2026-26962: rack: improper unfolding of folded multipart headers can lead to downstream header     injection and       response splitting(bsc#1261471).
    - CVE-2026-34763: rack: unescaped regex interpolation of configured root path can lead to root directory     disclosure       (bsc#1261406).
    - CVE-2026-34785: rack: prefix matching logic can lead to the exposure of unintended files under the     static root       (bsc#1261417).
    - CVE-2026-34786: rack: URL-encoded path mismatch can lead to `header_rules` bypass (bsc#1261426).
    - CVE-2026-34826: rack: missing individual byte range limit checks when parsing HTTP `Range` headers can     lead to       excessive resource consumption and a denial of service (bsc#1261436).
    - CVE-2026-34829: rack: multipart parsing without `Content-Length` header can lead to unbounded chunked     file uploads       and a denial of service (bsc#1261447).
    - CVE-2026-34230: rack: quadratic complexity when processing of wildcard `Accept-Encoding` headers can     lead to a denial       of service (bsc#1261388).
    - CVE-2026-34830: rack: improper sanitization of the `X-Accel-Mapping` request header can lead to the     exposure of       unintended files via `X-Accel-Redirect` (bsc#1261458).
    - CVE-2026-34831: rack: `Content-Length` header and body byte size mismatch when creating error responses     can lead to       incorrect HTTP response framing (bsc#1261466).

    Other updates and bugfixes:

    - Fix ReDoS in `Addressable`.
    - Fix out-of-bounds read in `rdiscount`.

Tenable has extracted the preceding description block directly from the SUSE 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 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 3.2.0 or later but prior to 3.2.6.
It is, therefore, affected by a header injection vulnerability:

  - Rack::Multipart::Parser unfolds folded multipart part headers incorrectly, preserving embedded CRLF     in parsed parameter values instead of removing folded line break. Applications reusing these values     in HTTP response headers may be vulnerable to header injection or response splitting. (CVE-2026-26962)

Note that Nessus has not tested for this issue 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. From version 3.2.0 to before version 3.2.6,     Rack::Multipart::Parser unfolds folded multipart part headers incorrectly. When a multipart header     contains an obs-fold sequence, Rack preserves the embedded CRLF in parsed parameter values such as     filename or name instead of removing the folded line break during unfolding. As a result, applications     that later reuse those parsed values in HTTP response headers may be vulnerable to downstream header     injection or response splitting. This issue has been patched in version 3.2.6. (CVE-2026-26962)

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

ID	Name	Product	Family	Severity
313640	SUSE SLES15 Security Update : rmt-server (SUSE-SU-2026:1745-1)	Nessus	SuSE Local Security Checks	high
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
305960	Ruby Rack 3.2.x < 3.2.6 Header Injection Vulnerability	Nessus	Misc.	medium
304928	Linux Distros Unpatched Vulnerability : CVE-2026-26962	Nessus	Misc.	medium

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CVE-2026-26962

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