Time-of-check Time-of-use (TOCTOU) Race Condition in Contao - #VU165874
Published: November 11, 2026
Vulnerability identifier: #VU165874
CSH Severity: Low
CVSS v4: 2.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-367
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to bypass private-network restrictions through server-side request forgery and disclose sensitive information.
The vulnerability exists due to a time-of-check time-of-use race condition in Contao's NoPrivateNetworkExceptRootPagesHttpClient when handling cached hosts without pinning the checked IP address. A remote user can manipulate hostname resolution between validation and connection to direct requests to private-network resources and potentially disclose sensitive information.
Affected software
Contao
Remediation
Install security update from vendor's website.
Contao - addressed in versions 5.3.54, 5.7.17, 6.0.6