Vulnerability Instance

Nokogiri patches vendored libxml2 to resolve multiple CVEs
## Summary

Nokogiri v1.18.9 patches the vendored libxml2 to address
CVE-2025-6021, CVE-2025-6170, CVE-2025-49794, CVE-2025-49795,
and CVE-2025-49796.

## Impact and severity

### CVE-2025-6021

A flaw was found in libxml2's xmlBuildQName function, where integer
overflows in buffer size calculations can lead to a stack-based
buffer overflow. This issue can result in memory corruption or a
denial of service when processing crafted input.

NVD claims a severity of 7.5 High
(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Fixed by applying https://gitlab.gnome.org/GNOME/libxml2/-/commit/17d950ae

### CVE-2025-6170

A flaw was found in the interactive shell of the xmllint command-line
tool, used for parsing XML files. When a user inputs an overly long
command, the program does not check the input size properly, which
can cause it to crash. This issue might allow attackers to run
harmful code in rare configurations without modern protections.

NVD claims a severity of 2.5 Low
(CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L)

Fixed by applying https://gitlab.gnome.org/GNOME/libxml2/-/commit/5e9ec5c1

### CVE-2025-49794

A use-after-free vulnerability was found in libxml2. This issue
occurs when parsing XPath elements under certain circumstances when
the XML schematron has the <sch:name path="..."/> schema elements.
This flaw allows a malicious actor to craft a malicious XML document
used as input for libxml, resulting in the program's crash using
libxml or other possible undefined behaviors.

NVD claims a severity of 9.1 Critical
(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H)

Fixed by applying https://gitlab.gnome.org/GNOME/libxml2/-/commit/81cef8c5

### CVE-2025-49795

A NULL pointer dereference vulnerability was found in libxml2 when
processing XPath XML expressions. This flaw allows an attacker to
craft a malicious XML input to libxml2, leading to a denial of service.

NVD claims a severity of 7.5 High
(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Fixed by applying https://gitlab.gnome.org/GNOME/libxml2/-/commit/62048278

### CVE-2025-49796

A vulnerability was found in libxml2. Processing certain sch:name
elements from the input XML file can trigger a memory corruption
issue. This flaw allows an attacker to craft a malicious XML input
file that can lead libxml to crash, resulting in a denial of service
or other possible undefined behavior due to sensitive data being
corrupted in memory.

NVD claims a severity of 9.1 Critical
(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H)

Fixed by applying https://gitlab.gnome.org/GNOME/libxml2/-/commit/81cef8c5

## Affected Versions

- Nokogiri < 1.18.9 when using CRuby (MRI) with vendored libxml2

## Patched Versions

- Nokogiri >= 1.18.9

## Mitigation

Upgrade to Nokogiri v1.18.9 or later.

Users who are unable to upgrade Nokogiri may also choose a more
complicated mitigation: compile and link Nokogiri against patched
external libxml2 libraries which will also address these same issues.