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LibexpatApplication · Libexpat Project

CVE-2025-66382

MEDIUM · 5.5 CVSS v3.1 Published 2025-11-28
Fix available
A fix is available. Upgrade to after 2.7.3 or later.
See remediation →
58/100
Remediation priority · Elevated
No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In libexpat through 2.7.3, a crafted file with an approximate size of 2 MiB can lead to dozens of seconds of processing time.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A denial-of-service vulnerability in libexpat through version 2.7.3 allows a specially crafted XML file of approximately 2 MiB to cause excessive parsing time (dozens of seconds), likely due to quadratic or worse algorithmic complexity in the XML parser's handling of certain constructs.

MitigationUpdate libexpat to a version beyond 2.7.3 that contains the fix, or implement parsing timeouts and resource limits when processing untrusted XML input.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
LibexpatApplication
Affected:<= 2.7.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify libexpat version
    Run 'pkg-config --modversion expat' or check the shared library file: 'ls -la /usr/lib/libexpat*' and look for version symbols. On Windows, check 'expat.h' header version or the DLL properties.
    Affected if The installed version is 2.7.3 or lower.
  2. Find libexpat library files
    Locate libexpat using 'find /usr -name "*expat*" -type f' (Linux), 'locate libexpat' (if indexed), or check common paths like /usr/lib/, /usr/local/lib/, C:\Windows\System32\.
    Affected if libexpat library files exist on the system and are used by any application.
  3. Identify processes using libexpat
    Run 'lsof +c 0 | grep -i expat' or 'pmap -p <pid>' on running processes to find applications linked against libexpat. Check application dependencies with 'ldd <application>' or 'dumpbin /dependents <application>.exe' (Windows).
    Affected if Any application or service links against libexpat and processes XML input.
  4. Determine if XML parsing handles external input
    Review application documentation, source code, or configuration to identify if the application accepts XML from untrusted sources (file uploads, API requests, network data).
    Affected if The application parses XML from untrusted or external sources using libexpat.
  5. Check for resource limits on XML processing
    Inspect application code or runtime configuration for XML parser timeouts, entity expansion limits, or max parse depth settings. Look for XML_SetElementHandler, XML_SetCharacterDataHandler usage patterns.
    Affected if No timeout or resource limits are configured on the XML parser, and untrusted XML is processed.

A system is affected if libexpat version 2.7.3 or lower is installed AND any application parses untrusted XML using that library without timeouts or resource limits.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 2.7.3
Interim mitigation

Update libexpat to a version beyond 2.7.3 that contains the fix, or implement parsing timeouts and resource limits when processing untrusted XML input.

Recommended fix Moderate confidence

libexpat 2.7.4 or later

  1. 1. Identify all systems and applications that use libexpat library version 2.7.3 or earlier
  2. 2. Obtain the latest stable release of libexpat from the official source (github.com/libexpat/libexpat)
  3. 3. Compile and install the newer version of libexpat following standard build procedures (typically ./configure, make, make install)
  4. 4. Rebuild any applications that link against libexpat to ensure they use the updated library
  5. 5. Verify the installed version is greater than 2.7.3 using expat version check or pkg-config
  6. 6. Test that XML parsing functionality continues to work correctly with the updated library
  7. 7. Redeploy the updated library to all affected systems
Caveat Minor: Ensure any application-specific XML parsing behavior remains compatible after upgrade; standard API should be unchanged

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Libexpat Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-66382 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data