⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● High · CVSS 8.6

How to Fix CVE-2026-25990: Command Injection in Pillow

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 8.6 - High
Actively exploited?Not currently listed in CISA KEV
Affected>= 10.3.0, < 12.1.1
Fixed in12.1.1.
Type (CWE)CWE-787: Out-of-bounds Write

What is CVE-2026-25990?

CVE-2026-25990 is an OS command injection bug in Pillow. The product builds a shell command from untrusted input without escaping, so injected metacharacters run as the service account, often root or SYSTEM. Vendor description: Pillow is a Python imaging library. From 10.3.0 to before 12.1.1, an out-of-bounds write may be triggered when loading a specially crafted PSD image.

Why this CVE matters

Command injection in a network appliance or management console gives the attacker the same privileges as the service account, which is usually root or SYSTEM. From there, persistence, lateral movement, and credential theft follow with off-the-shelf tooling.

For deployments of Pillow that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

Open Pillow's About dialog or run the vendor-documented version-check command. Compare the result against the affected ranges in the advisory.

How to fix CVE-2026-25990

  1. Read the vendor advisory in full: https://github.com/python-pillow/Pillow/security/advisories/GHSA-cfh3-3jmp-rvhc
  2. Upgrade Pillow to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Rotate any credentials, API keys, or session tokens that the vulnerable service touched. An unauthenticated RCE-class flaw means anything the process could see should be treated as exposed.
  5. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  6. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

Patched-version commands

Vendor advisory: https://github.com/python-pillow/Pillow/security/advisories/GHSA-cfh3-3jmp-rvhc

Affected: Pillow: >= 10.3.0, < 12.1.1

Patched in: 12.1.1


# Vendor advisory: https://github.com/python-pillow/Pillow/security/advisories/GHSA-cfh3-3jmp-rvhc

# Patch in-place.
python -m pip install --upgrade "pillow>=12.1.1"

# Pin in requirements.txt and re-sync for reproducible builds.
sed -i 's/^pillow==.*/pillow==12.1.1/' requirements.txt
python -m pip install -r requirements.txt

# Verify.
python -m pip show pillow | grep -i version


# Same flow on Windows.
python -m pip install --upgrade "pillow>=12.1.1"
python -m pip show pillow

Verify the fix landed


# Vendor advisory: https://github.com/python-pillow/Pillow/security/advisories/GHSA-cfh3-3jmp-rvhc
# Post-patch verification (replace <service> with the real service unit).
journalctl -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

# Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
# It should no longer flag CVE-2026-25990 on the patched target.

If you cannot patch immediately

Restrict access to the management or affected endpoint at the network layer. If the vendor lists a configuration toggle that disables the vulnerable feature, use it until you can patch.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for unexpected administrator accounts in Pillow, scheduled tasks or cron jobs you did not create, new files in web-accessible directories, and outbound connections to addresses not in your baseline. Suspicious requests to the vulnerable endpoint immediately followed by successful 200-class responses with unusually large bodies are a strong indicator of exploitation.

Frequently asked questions

Is CVE-2026-25990 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Will a WAF or IDS rule fully mitigate CVE-2026-25990?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

Do I need to assume compromise if my Pillow was internet-facing and unpatched?

For an unauthenticated RCE-class flaw exposed to the public internet during the known exploitation window, yes. Review logs, rotate credentials the process could access, and look for unexpected accounts, scheduled tasks, or outbound connections.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*