Pillow BdfFontFile: Image.new() called without _decompression_bomb_check() — bomb protection bypass via font loading

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-55379: 0.52% estimated exploitation activity in the next 30 days; percentile 44.36 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary PIL/BdfFontFile.py bdfchar() (lines 84–88) reads the BBX width height field from a BDF font file and passes the dimensions directly to Image.new() without calling Image.decompressionbombcheck(). This completely bypasses Pillow's documented decompression bomb protection. Image.open() enforces MAXIMAGEPIXELS = 89,478,485 and raises DecompressionBombError for images exceeding 2 × MAX = 178,956,970 pixels. The BDF font loading path calls Image.new() directly, which only calls checksize() (validates = 0) — no pixel count limit. Vulnerable code (PIL/BdfFontFile.py lines 84–88): Attack trigger: A BDF glyph with BBX 20000 20000 and an empty BITMAP section causes Image.frombytes() to raise ValueError, then Image.new("1", (20000, 20000)) allocates 50 MB of C-heap silently. Image.open() would raise DecompressionBombError for the same dimensions. Steps to reproduce Minimal malicious BDF file (270 bytes): Proof of Concept script: Expected output: Amplified attack (multiple glyphs): A BDF…

Published by the source

20 Jul 2026, 21:13 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:49 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-45hq-cxwh-f6vc

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-45hq-cxwh-f6vc

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-55379

Advisory: Pillow `BdfFontFile`: `Image.new()` called without `_decompression_bomb_check()` — bomb protection bypass via font loading
IDs: CVE-2026-55379, GHSA-45hq-cxwh-f6vc
Record: https://patchnext.com/advisories/cve-2026-55379 (revision 2, source checked 26 Oct 2026, 13:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pillow 12.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pillow: affected < 12.3.0; fixed in 12.3.0

## Suggested inspection (read-only)
- `python -m pip show pillow`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pillow.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-45hq-cxwh-f6vc (OSV record GHSA-45hq-cxwh-f6vc lists affected ranges: PyPI pillow >=0 <12.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-45hq-cxwh-f6vc (GitHub-reviewed advisory GHSA-45hq-cxwh-f6vc lists affected ranges: PyPI pillow >=0 <12.3.0)

Commands are suggestions: review each one before running it.