CVE-2026-107844 contao CVE debrief

Who should care

Defenders responsible for Contao installations, particularly those using versions 5.0.0 to 5.3.50 and 5.7.12, should assess exposure and apply patches. They should also review compensating controls for exposed systems, monitor for suspicious requests, and track exceptions and retest remediated assets.

Why it matters

CVE-2026-107844 is a path traversal vulnerability in Contao's images controller that can lead to unauthorized file disclosure and debug response path disclosure. Defenders should prioritize verifying exposure and applying patches for Contao versions 5.0.0 to 5.3.50 and 5.7.12.

• Path traversal can lead to unauthorized file disclosure
• Debug responses can disclose absolute filesystem paths
• Existence of arbitrary paths can be revealed

Technical summary

The vulnerability is caused by the ImagesController joining the user-controlled path parameter to the configured image target directory with Path::join() but not using Path::isBasePath() to verify that the canonical path remains inside that directory. This allows an unauthenticated request to return files under the project directory through BinaryFileResponse when their names use an extension allowed by contao.image.valid_extensions. The route can also reveal whether arbitrary paths exist, and debug responses can disclose absolute filesystem paths.

Defensive priority

Defenders should prioritize verifying exposure and applying patches for Contao versions 5.0.0 to 5.3.50 and 5.7.12.

Recommended defensive actions

• Verify Contao version and apply patches if necessary
• Restrict access to the images controller
• Monitor for suspicious requests
• Review compensating controls for exposed systems while remediation is scheduled and verified
• 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
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and source item provide details on the vulnerability, affected versions, and fixed versions. The vulnerability allows an unauthenticated request to return files under the project directory through BinaryFileResponse when their names use an extension allowed by contao.image.valid_extensions. The route can also reveal whether arbitrary paths exist, and debug responses can disclose absolute filesystem paths, but paths below the upload directory were not shown to be readable. Defenders should verify exposure and apply 5.3.1

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.