Summary
Pillow has a PDF Parsing Trailer Infinite Loop (DoS)
Workarounds
Use any version but the affected versions: >= 4.2.0, < 12.2.0
Resources
Impact
An attacker can supply a malicious PDF that causes the process to hang indefinitely, consuming 100% CPU and making the application unresponsive.
CVE-2026-42310 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (12.2.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Patched version: 12.2.0.
PdfParser (introduced in Pillow 4.2.0) follows Prev pointers in PDF trailers to read cross-reference sections. If a
trailer's Prev pointer references an offset that has already been processed, either pointing to itself or forming a
longer cycle, the parser enters an infinite loop. Pillow now tracks previously processed trailer offsets and raises an
error if a cycle is detected.
Frequently Asked Questions
- What is CVE-2026-42310? CVE-2026-42310 is a medium-severity security vulnerability in pillow (pip), affecting versions >= 4.2.0, < 12.2.0. It is fixed in 12.2.0.
- How severe is CVE-2026-42310? CVE-2026-42310 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of pillow are affected by CVE-2026-42310? pillow (pip) versions >= 4.2.0, < 12.2.0 is affected.
- Is there a fix for CVE-2026-42310? Yes. CVE-2026-42310 is fixed in 12.2.0. Upgrade to this version or later.
- Is CVE-2026-42310 exploitable, and should I be worried? Whether CVE-2026-42310 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-42310 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-42310? Upgrade
pillowto 12.2.0 or later.