CVE-2026-106443 Kozea CVE debrief

Who should care

Defenders responsible for systems using WeasyPrint, especially those with Ghostscript installed, should assess potential exposure and impact. This includes operators, platform administrators, vulnerability management teams, and security teams who need to prioritize verifying exposure, assessing potential impact, and implementing compensating controls to restrict image input formats.

Why it matters

Defenders should prioritize verifying exposure and assessing potential impact due to remote code execution potential and unrestricted image input formats.

• Remote code execution potential when Ghostscript is installed
• Unrestricted image input formats allow attacker-controlled PostScript
• Exposure in systems using WeasyPrint with Ghostscript

Technical summary

WeasyPrint passes fetched image bytes directly to Pillow's generic format dispatcher without restricting the input format. When Ghostscript is installed on the host, Pillow's EpsImagePlugin invokes it to rasterize attacker-controlled EPS/PS input, potentially leading to remote code execution. The image pipeline reads an external response and hands the raw bytes to Pillow's format-agnostic Image.open, with no allowlist of safe raster formats. This issue allows any content that can supply an image to WeasyPrint (an <img> URL, CSS image value, SVG image reference, or data URI) to drive untrusted PostScript into an external interpreter.

Defensive priority

Defenders should prioritize verifying exposure and assessing potential impact, focusing on systems using WeasyPrint with Ghostscript installed.

Recommended defensive actions

• Verify WeasyPrint versions and configurations to ensure they are not vulnerable
• Assess potential impact on systems using WeasyPrint with Ghostscript installed
• Implement compensating controls to restrict image input formats
• Monitor for potential exploitation attempts
• Review vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The issue was found during a pentest funded by the NLNnet foundation, conducted by Stefan Vink from Radically Open Security. WeasyPrint passes fetched image bytes directly to Pillow's generic format dispatcher without restricting the input format, which can lead to remote code execution when Ghostscript is installed on the host.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.