medium CVSS 5.5 EPSS <0.1%

CVE-2026-42310·Python vulnerability

Pillow is a Python imaging library. From version 4.2.0 to before version 12.2.0, an attacker can supply a malicious PDF that causes the process to hang indefinitely, consuming 100% CPU and making the application unresponsive. This issue has been patched in version 12.2.0.

Severity
medium
Software
Python
Fixed in
12.2.0
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 2% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

From: 4.2.0

Until: 12.2.0

Fixed in: 12.2.0

How to fix this CVE

Update the Pillow library to version 12.2.0 or later to resolve a denial-of-service vulnerability in PDF processing. Applications using Pillow versions 4.2.0 through 12.1.x should prioritize this update, as malicious PDF files can trigger infinite loops that consume CPU resources and render services unresponsive. Verify the update is applied and test PDF handling functionality after patching.

sudo dnf update python3-pillow

Defensia detects this vulnerability

How to check if you are affected

  1. Check the installed Pillow version: python3 -c "import PIL; print(PIL.__version__)"
  2. Identify Python processes handling PDF files: ps aux | grep -i pdf or check application logs for PDF processing modules
  3. Search system logs for CPU spikes during PDF processing: grep -i 'high cpu\|100%\|hang' /var/log/syslog /var/log/messages
  4. Verify the patch by re-running the version check command and confirming the version is 12.2.0 or later

FAQ

What is CVE-2026-42310?

This vulnerability affects the Pillow image library's PDF parsing module, allowing attackers to craft malicious PDF files that trigger algorithmic complexity issues. When processed, these PDFs cause the application to enter an infinite loop, consuming maximum CPU and freezing the service indefinitely.

Is CVE-2026-42310 being actively exploited?

No, this vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public exploits are currently available. However, the attack surface remains open for any system processing untrusted PDF documents.

What versions of Python are affected by CVE-2026-42310?

Pillow versions 4.2.0 through 12.1.x are vulnerable. The vulnerability is patched in Pillow 12.2.0 and later. Python itself is not directly affected; rather, applications using the vulnerable Pillow library are at risk.

How do I check if my server is vulnerable to CVE-2026-42310?

Run `python3 -c "import PIL; print(PIL.__version__)"` to check your installed Pillow version. If the version is between 4.2.0 and 12.1.x, your system is vulnerable.

Does Defensia detect CVE-2026-42310?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Pillow is installed on a monitored server, CVE-2026-42310 will appear in your dashboard with remediation steps.

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References

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