CVE-2026-55379 pillow vulnerability
Pillow is a Python imaging library. Prior to 12.3.0, PIL/BdfFontFile.py bdf_char() read the BBX width and height field from a BDF font file and passed attacker-controlled dimensions to Image.new() without calling Image._decompression_bomb_check(), bypassing Pillow's documented decompression bomb protection and allowing excessive memory allocation. This issue is fixed in version 12.3.0.
Quick answer
python pillow should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- Review vendor advisory for affected versions.
Fixed versions
- Apply the latest vendor-supported patched version.
How to fix it
Pillow is affected by CVE-2026-55379, a resource exhaustion risk. Pillow is a Python imaging library. The recommended remediation is to update to Pillow 12.3.0 or later. Until the update is complete, avoid loading untrusted BDF fonts and enforce image/font decompression limits before processing, review logs, and reduce exposure of the affected service, library, appliance, or trusted firmware path.
- Inventory every deployment, package, appliance, service, application dependency, trusted firmware image, and managed environment that uses Pillow.
- Confirm the installed version/build and compare it with versions prior to 12 and the source advisory for CVE-2026-55379.
- Apply the vendor-supported fix: update to Pillow 12.3.0 or later.
- If the update cannot be applied immediately, avoid loading untrusted BDF fonts and enforce image/font decompression limits before processing; disable unnecessary public access, file processing, authentication integrations, upload endpoints, or high-risk features until patched.
- Review application, appliance, reverse-proxy, WAF, package manager, authentication, trusted firmware, and audit logs for activity related to CVE-2026-55379.
- Rotate sessions, API tokens, service credentials, integration keys, signing keys, and administrator passwords if logs or affected data indicate compromise, code execution, credential exposure, or unauthorized access.
- Clear caches, restart affected services, rebuild affected containers or firmware images when appropriate, and remove temporary files, uploaded artifacts, stored payloads, or unsafe configuration created during exploitation attempts.
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Verify the fix
- Confirm Pillow now reports Pillow 12.3.0 or later or a later vendor-supported fixed release/build for the deployed branch.
- Verify the affected workflow no longer allows the behavior described in CVE-2026-55379, using a safe regression test, vendor validation method, dependency inventory, or appliance health check.
- Review logs after remediation for continued exploit attempts, authentication anomalies, denial-of-service symptoms, suspicious uploads, file access, deserialization attempts, or configuration changes.
- Rerun a Fixnx scan and any product-specific scanner, package audit, firmware inventory, appliance health check, or manual regression test relevant to the affected service.
- Document affected assets, fixed versions, mitigation decisions, validation evidence, and any cleanup, rebuild, or credential rotation performed.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-55379?
python pillow should be checked against the vendor advisory and trusted references linked on this page.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.