Package Instance

Nokogiri CSS selector tokenizer has regular expression backtracking
## Summary

Nokogiri's CSS selector tokenizer contains regular expressions whose construction may result in exponential regex backtracking on adversarial selectors. Three ReDoS vectors are addressed in this release:

1. String-literal tokenization on certain unterminated quoted-string input.
2. String-literal tokenization on a separate class of hex-escape-rich input.
3. Identifier tokenization on hex-escape-rich input.

The public CSS selector methods that funnel through the affected tokenizer are `Nokogiri::CSS.xpath_for`, `Node#css`, `Node#at_css`, `Searchable#search`, and `CSS::Parser#parse`.


## Mitigation

Upgrade to Nokogiri `>= 1.19.3`.

If users are unable to upgrade, two options are available:

- Avoid the use of attacker-controlled text in CSS selectors. Applications that only pass developer-authored selectors to Nokogiri are not directly exposed.
- Set global `Regexp.timeout` (Ruby 3.2+, JRuby 9.4+) to bound parse time.

## Severity

The Nokogiri maintainers have evaluated this as **High Severity** (CVSS 7.5, `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`).

An attacker able to inject user-supplied text into a CSS selector parse method can cause exponential backtracking, resulting in a potential denial of service.


## Resources

- [CWE-1333: Inefficient Regular Expression Complexity](https://cwe.mitre.org/data/definitions/1333.html)


## Credit

Vector 1 was responsibly reported by @colby-swandale. Vectors 2 and 3 were discovered by @flavorjones during the response to the original report.

Nokogiri does not check the return value from xmlC14NExecute
Nokogiri's CRuby extension fails to check the return value from `xmlC14NExecute` in the method `Nokogiri::XML::Document#canonicalize` and `Nokogiri::XML::Node#canonicalize`. When canonicalization fails, an empty string is returned instead of raising an exception. This incorrect return value may allow downstream libraries to accept invalid or incomplete canonicalized XML, which has been demonstrated to enable signature validation bypass in SAML libraries.

JRuby is not affected, as the Java implementation correctly raises `RuntimeError` on canonicalization failure.

Nokogiri XSLT transform has a memory leak
## Summary

Nokogiri's `Nokogiri::XSLT::Stylesheet#transform` leaks a small heap allocation when passed a Ruby string parameter containing a null byte.

For applications that pass attacker-controlled input through `XSLT.transform` parameters, this may be a vector for a denial of service attack against long-running processes.


## Mitigation

Upgrade to Nokogiri `>= 1.19.3`.

Users may also be able to mitigate this issue without upgrading by validating untrusted transform parameters before passing them to `Nokogiri::XSLT::Stylesheet#transform`.


## Severity

The Nokogiri maintainers have evaluated this as **Moderate Severity**, CVSS 5.3.

Each leaked allocation is approximately 24–32 bytes, so meaningful memory growth requires sustained attacker-controlled traffic at high call rates. The bug does not cause memory corruption, information disclosure, or any change in the behavior of the transform itself, and the string-handling exception is raised as expected.

Applications that do not pass raw attacker-controlled bytes to XSLT parameters are unlikely to be affected in practice.


## Resources

- [CWE-401: Missing Release of Memory after Effective Lifetime](https://cwe.mitre.org/data/definitions/401.html)


## Credit

This vulnerability was responsibly reported by @Captainjack-kor.

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.

Nokogiri updates packaged libxml2 to v2.13.8 to resolve CVE-2025-32414 and CVE-2025-32415
## Summary

Nokogiri v1.18.8 upgrades its dependency libxml2 to
[v2.13.8](https://gitlab.gnome.org/GNOME/libxml2/-/releases/v2.13.8).

libxml2 v2.13.8 addresses:

- CVE-2025-32414
  - described at https://gitlab.gnome.org/GNOME/libxml2/-/issues/889
- CVE-2025-32415
  - described at https://gitlab.gnome.org/GNOME/libxml2/-/issues/890

## Impact

### CVE-2025-32414: No impact

In libxml2 before 2.13.8 and 2.14.x before 2.14.2, out-of-bounds
memory access can occur in the Python API (Python bindings) because
of an incorrect return value. This occurs in xmlPythonFileRead and
xmlPythonFileReadRaw because of a difference between bytes and characters.

**There is no impact** from this CVE for Nokogiri users.

### CVE-2025-32415: Low impact

In libxml2 before 2.13.8 and 2.14.x before 2.14.2,
xmlSchemaIDCFillNodeTables in xmlschemas.c has a heap-based buffer
under-read. To exploit this, a crafted XML document must be validated
against an XML schema with certain identity constraints, or a
crafted XML schema must be used.

In the upstream issue, further context is provided by the maintainer:

> The bug affects validation against untrusted XML Schemas (.xsd)
> and validation of untrusted documents against trusted Schemas if
> they make use of xsd:keyref in combination with recursively
> defined types that have additional identity constraints.

MITRE has published a severity score of 2.9 LOW
(CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L) for this CVE.