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High, CVSS 7.1amended

Pillow: TarIO negative size field causes infinite CPU-spin loop

CVE-2026-96642GHSA-3j72-p6qg-6xp7

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (pillow 13.0.0; pillow 13.0.0), 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

  • Bitnami pillow

    Affected
    < 13.0.0
    Fixed in
    13.0.0

  • PyPI pillow

    Affected
    < 13.0.0
    Fixed in
    13.0.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-96642: 0.34% estimated exploitation activity in the next 30 days; percentile 28.05 (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.

Summary `TarIO.init` does not check that a tar header's size field is positive. A crafted header with a negative size makes it seek backward onto itself. This causes an infinite loop that uses 100% CPU and never returns.

Details `TarIO.init` reads 512-byte tar headers one at a time, looking for a member with a given name. For each header it reads the size field and skips ahead to the next header: ```python size = int(s[124:135], 8) ... self.fh.seek((size + 511) & (~511), io.SEEK_CUR) ``` There is no check that size is zero or more. A tar header can set this field to a negative octal value. For size = -512, the seek offset comes out to exactly -512, which cancels the 512 bytes the loop had just read. The file position goes right back to where this loop step started. The loop only stops on end of file or when a header name starts with a null byte. Neither happens, since the same header keeps showing up again. The loop never ends on its own.

Steps to reproduce This…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 10 · amended ·

    Amended from osv record BIT-pillow-2026-96642

  2. Revision 9 · amended ·

    Amended from osv record PYSEC-2026-4341

  3. Revision 8 · amended ·

    Amended from osv record GHSA-3j72-p6qg-6xp7

  4. Revision 7 · amended ·

    Amended from osv record PYSEC-2026-4341

  5. Revision 6 · amended ·

    Amended from osv record GHSA-3j72-p6qg-6xp7

  6. Revision 5 · amended ·

    Amended from ghsa record GHSA-3j72-p6qg-6xp7

  7. Revision 4 · amended ·

    Amended from ghsa record GHSA-3j72-p6qg-6xp7

  8. Revision 3 · amended ·

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

  9. Revision 2 · amended ·

    Amended from osv record GHSA-3j72-p6qg-6xp7

  10. Revision 1 · created ·

    Published from ghsa record GHSA-3j72-p6qg-6xp7

Agent brief

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

# Patch Next advisory brief: CVE-2026-96642

Advisory: Pillow: TarIO negative size field causes infinite CPU-spin loop
IDs: CVE-2026-96642, GHSA-3j72-p6qg-6xp7
Record: https://patchnext.com/advisories/cve-2026-96642 (revision 10, source checked 30 Oct 2026, 07:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pillow 13.0.0; pillow 13.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Bitnami pillow: affected < 13.0.0; fixed in 13.0.0
- PyPI pillow: affected < 13.0.0; fixed in 13.0.0

## Suggested inspection (read-only)
- Bitnami pillow: check the installed version with your package manager.
- `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://github.com/advisories/GHSA-3j72-p6qg-6xp7 (GitHub-reviewed advisory GHSA-3j72-p6qg-6xp7 lists affected ranges: PyPI pillow >=0 <13.0.0)
- Verified: https://osv.dev/vulnerability/GHSA-3j72-p6qg-6xp7 (OSV record GHSA-3j72-p6qg-6xp7 lists affected ranges: PyPI pillow >=0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/PYSEC-2026-4341 (OSV record PYSEC-2026-4341 lists affected ranges: PyPI pillow >=0 <13.0.0 (fixed))
- Verified: https://osv.dev/vulnerability/BIT-pillow-2026-96642 (OSV record BIT-pillow-2026-96642 lists affected ranges: Bitnami pillow >=0 <13.0.0 (fixed))

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