CVE-2017-9233 — XML External Entity vulnerability in libexpat 2

XML External Entity vulnerability in libexpat 2.2.0 and earlier (Expat XML Parser Library) allows attackers to put the parser in an infinite loop using a malformed external entity definition from an external DTD.

01What is this vulnerability?

XML External Entity vulnerability in libexpat 2.2.0 and earlier (Expat XML Parser Library) allows attackers to put the parser in an infinite loop using a malformed external entity definition from an external DTD.

02Affected products

No structured affected-product list available — see references below for vendor advisories.

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2017-07-25T20:29:00.220
• Last modified: 2026-10-08T21:17:06.167

09References

• www.debian.org — http://www.debian.org/security/2017/dsa-3898
• www.openwall.com — http://www.openwall.com/lists/oss-security/2017/06/17/7
• www.securityfocus.com — http://www.securityfocus.com/bid/99276
• www.securitytracker.com — http://www.securitytracker.com/id/1039427
• github.com — https://github.com/libexpat/libexpat/blob/master/expat/Changes
• libexpat.github.io — https://libexpat.github.io/doc/cve-2017-9233/
• lists.apache.org — https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e3…
• lists.apache.org — https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8…
• support.apple.com — https://support.apple.com/HT208112
• support.apple.com — https://support.apple.com/HT208113