pillow-heif: Integer Overflow in Encode Path Buffer Validation Leads to Heap Out-of-Bounds Read

Exploitation

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

CVSS 4.0

5.5 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-28231: 0.70% estimated exploitation activity in the next 30 days; percentile 53.33 (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 An integer overflow in the encode path buffer validation of pillowheif.c allows an attacker to bypass bounds checks by providing large image dimensions, resulting in a heap out-of-bounds read. This can lead to information disclosure (server heap memory leaking into encoded images) or denial of service (process crash). No special configuration is required — this triggers under default settings. Details The buffer validation in CtxWriteImageaddplane(), CtxWriteImageaddplanela(), and CtxWriteImageaddplanel() uses 32-bit int multiplication to check whether the input buffer is large enough: Both stridein and height are declared as int (32-bit signed). When their product exceeds INTMAX (2,147,483,647), the multiplication overflows before the comparison with buffer.len (which is Pyssizet, 64-bit). The overflowed value wraps to zero or a negative number, causing the bounds check to pass incorrectly. For example, with stridein = 196608 (65536 × 3 for RGB) and height = 65536: - True…

Published by the source

20 Jul 2026, 19:08 UTC

Last modified by the source

20 Jul 2026, 19:15 UTC

Source last checked

26 Oct 2026, 13:49 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5gjj-6r7v-ph3x

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-5gjj-6r7v-ph3x

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# Patch Next advisory brief: CVE-2026-28231

Advisory: pillow-heif: Integer Overflow in Encode Path Buffer Validation Leads to Heap Out-of-Bounds Read
IDs: CVE-2026-28231, GHSA-5gjj-6r7v-ph3x
Record: https://patchnext.com/advisories/cve-2026-28231 (revision 3, 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: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pi-heif 1.3.0; pillow-heif 1.3.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pi-heif: affected < 1.3.0; fixed in 1.3.0
- PyPI pillow-heif: affected < 1.3.0; fixed in 1.3.0

## Suggested inspection (read-only)
- `python -m pip show pi-heif`: prints the installed version. Run with the environment that serves production active.
- `python -m pip show pillow-heif`: 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 pi-heif, pillow-heif.
- 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-5gjj-6r7v-ph3x (OSV record GHSA-5gjj-6r7v-ph3x lists affected ranges: PyPI pi-heif >=0 =0 <1.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-5gjj-6r7v-ph3x (GitHub-reviewed advisory GHSA-5gjj-6r7v-ph3x lists affected ranges: PyPI pi-heif >=0 =0 <1.3.0)

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