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High, CVSS 7.5amended

Pillow PcfFontFile._load_bitmaps(): Image.frombytes() called without _decompression_bomb_check() — bomb protection bypass via PCF font loading

CVE-2026-54059GHSA-8v84-f9pq-wr9x

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (pillow 12.3.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI pillow

    Affected
    < 12.3.0
    Fixed in
    12.3.0

Sources

Severity and exploitation
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-2026-54059: 0.41% estimated exploitation activity in the next 30 days; percentile 35.26 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Description PIL/PcfFontFile.py loadbitmaps() (line 227) reads glyph dimensions from the PCF METRICS section and passes them directly to Image.frombytes() without calling Image.decompressionbombcheck(). Dimensions originate from unsigned 16-bit values: Maximum exploitable pixel count: 65,535 × 131,070 = 8,589,734,450 pixels — 48× the DecompressionBombError threshold. Vulnerable code (PIL/PcfFontFile.py line 224–227): Image.frombytes() calls Image.new() first (allocating the full C-heap buffer), then attempts to fill it. This creates two distinct attack paths: - Persistent attack: Provide matching bitmap data → frombytes() succeeds → image stored in font.glyph[ch] permanently - Transient attack: Provide a 148-byte PCF file with large declared dimensions but no data → Image.new() allocates the full buffer → ValueError → buffer freed → but the spike occurs before Python can respond Steps to reproduce Proof of Concept script: Expected output: Amplification table: | PCF file | Glyph dims |…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-8v84-f9pq-wr9x

  2. Revision 1 · created ·

    Published from osv record GHSA-8v84-f9pq-wr9x

Agent brief

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# Patch Next advisory brief: CVE-2026-54059

Advisory: Pillow `PcfFontFile._load_bitmaps()`: `Image.frombytes()` called without `_decompression_bomb_check()` — bomb protection bypass via PCF font loading
IDs: CVE-2026-54059, GHSA-8v84-f9pq-wr9x
Record: https://patchnext.com/advisories/cve-2026-54059 (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-8v84-f9pq-wr9x (OSV record GHSA-8v84-f9pq-wr9x lists affected ranges: PyPI pillow >=0 <12.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-8v84-f9pq-wr9x (GitHub-reviewed advisory GHSA-8v84-f9pq-wr9x lists affected ranges: PyPI pillow >=0 <12.3.0)

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