high CVSS 7.5

CVE-2026-59200·Python vulnerability

Pillow is a Python imaging library. From 5.1.0 until 12.3.0, PdfParser.PdfStream.decode() in PIL/PdfParser.py calls zlib.decompress() with bufsize set to the PDF stream Length field without bounding the decompressed output size, allowing a crafted FlateDecode PDF stream to exhaust memory from a small file. This issue is fixed in version 12.3.0.

Severity
high
Software
Python
Fixed in
12.3.0
Published
2026-07-14

Affected versions

From: 5.1.0

Until: 12.3.0

Fixed in: 12.3.0

How to fix this CVE

Update Python's Pillow imaging library to version 12.3.0 or later to patch a memory exhaustion vulnerability in PDF stream decompression. The vulnerability allows specially crafted PDF files to consume excessive memory, potentially causing denial of service. Immediately apply patches to all systems processing untrusted PDF files through Python applications.

sudo dnf update python3-pillow

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed Pillow version: python3 -c 'import PIL; print(PIL.__version__)'
  2. Identify Python applications that process PDF files: grep -r 'PdfParser\|PIL.PdfImagePlugin' /opt /home /srv --include='*.py' 2>/dev/null
  3. Search system logs for memory exhaustion events during PDF processing: journalctl -u {service_name} | grep -i 'memory\|oom\|killed'
  4. Verify patched version by running: python3 -c 'import PIL; assert PIL.__version__ >= "12.3.0", "Vulnerable version detected"'

FAQ

What is CVE-2026-59200?

A memory exhaustion vulnerability in Pillow's PDF stream decoder that fails to validate decompression output sizes, allowing attackers to trigger out-of-memory conditions by submitting specially crafted PDF files with FlateDecode streams.

Is CVE-2026-59200 being actively exploited?

No, there are currently no known active exploits or CISA KEV listings for this vulnerability, but the low barrier to exploitation warrants prompt patching.

What versions of Python are affected by CVE-2026-59200?

Pillow versions 5.1.0 through 12.2.0 are vulnerable; Python 3.x environments using these Pillow versions are affected. The vulnerability is resolved in Pillow 12.3.0 and later.

How do I check if my server is vulnerable to CVE-2026-59200?

Run: python3 -c 'import PIL; v = tuple(map(int, PIL.__version__.split("."))); print("VULNERABLE" if (5,1,0) <= v < (12,3,0) else "PATCHED")' and review which applications depend on Pillow for PDF handling.

Does Defensia detect CVE-2026-59200?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Python and Pillow are installed on a monitored server, CVE-2026-59200 will appear in your dashboard with remediation steps.

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References

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