Is CVE-2026-77139 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-77139 being exploited in the wild.

How severe is CVE-2026-77139?

Informational severity, with a CVSS score of 6.5, published 25 August 2026.

Which products and versions are affected?

Typo3 Mask 8.3.11 and below, 9.0.0 - 9.0.10.

Is there a fix for CVE-2026-77139?

A patch was published on 2026-08-25: Versions 8.3.12 and 9.0.11 available Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-77139 attacked?

It is attacked over the network.

Am I affected by CVE-2026-77139?

Check whether you run Typo3 Mask at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-77139: TYPO3 Mask extension path traversal in template handling

CVE-2026-77139 · Severity: info · CVSS 6.5 · Published 2026-08-25

The Mask extension for TYPO3 (a popular open-source content management system) fails to properly validate user-supplied template file names, allowing authenticated backend administrators to exploit path traversal sequences to create or delete HTML files outside the intended template directory. An attacker with legitimate backend access could manipulate file paths to overwrite critical system files or delete important templates, disrupting site operations or potentially compromising the integrity of the installation.

Vendors: Typo3.

Quick answers

Is CVE-2026-77139 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-77139 being exploited in the wild.
How severe is CVE-2026-77139?: Informational severity, with a CVSS score of 6.5, published 25 August 2026.
Which products and versions are affected?: Typo3 Mask 8.3.11 and below, 9.0.0 - 9.0.10.
Is there a fix for CVE-2026-77139?: A patch was published on 2026-08-25: Versions 8.3.12 and 9.0.11 available Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-77139 attacked?: It is attacked over the network.
Am I affected by CVE-2026-77139?: Check whether you run Typo3 Mask at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a path traversal (CWE-22) and improper path resolution (CWE-73) issue in the Mask extension's template file handling. When processing a client-supplied template element key, the extension fails to sanitize or validate the input before using it to construct file paths for saving and deleting .html template files. An authenticated backend user with access to the Mask module can supply a key containing sequences like "../" to traverse outside the configured template directory. The attack requires valid backend authentication and explicit access to the Mask module, limiting the exposure to trusted administrative users. Patch versions 8.3.12 and 9.0.11 have been released to address this issue.

Affected products

TYPO3 Mask 8.3.11 and below, 9.0.0 - 9.0.10

Timeline

2026-08-25: disclosed
2026-08-25: patched: Versions 8.3.12 and 9.0.11 available

References

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