Pillow: WindowsViewer.get_command() OS command injection via unescaped shell path

Exploitation

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

CVSS

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

EPSS

• CVE-2026-55798: 0.18% estimated exploitation activity in the next 30 days; percentile 7.48 (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.

1. Summary WindowsViewer.getcommand() constructs a cmd.exe shell command by directly embedding a file path into an f-string without escaping. The result is passed to subprocess.Popen(..., shell=True). Shell metacharacters in the file path — most importantly a double-quote (") that breaks out of the wrapping, followed by & — allow injection of arbitrary cmd.exe commands. The macOS equivalent (MacViewer) correctly applies shlex.quote() to the same parameter. The Linux equivalent (UnixViewer) does likewise. Windows is the only platform missing this protection, despite shlex.quote being already imported on line 21 of ImageShow.py. --- 2. Vulnerable Code File: src/PIL/ImageShow.py, lines 133–150 Contrast with macOS — SAFE (line 164–168): Cross-platform summary: | Platform | Class | shlex.quote()? | shell=True? | Safe? | |----------|----------------|------------------|---------------|-------| | macOS | MacViewer | Yes (line 168) | No (list args) | ✅ Yes | | Linux | UnixViewer | Yes (line…

Published by the source

20 Jul 2026, 21:14 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:49 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-4x4j-2g7c-83w6

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-4x4j-2g7c-83w6

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# Patch Next advisory brief: CVE-2026-55798

Advisory: Pillow: WindowsViewer.get_command() OS command injection via unescaped shell path
IDs: CVE-2026-55798, GHSA-4x4j-2g7c-83w6
Record: https://patchnext.com/advisories/cve-2026-55798 (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: Medium (CVSS 4.5)
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-4x4j-2g7c-83w6 (OSV record GHSA-4x4j-2g7c-83w6 lists affected ranges: PyPI pillow >=0 <12.3.0 (fixed))
- Verified: https://github.com/advisories/GHSA-4x4j-2g7c-83w6 (GitHub-reviewed advisory GHSA-4x4j-2g7c-83w6 lists affected ranges: PyPI pillow >=0 <12.3.0)

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