Summary
Acknowledgements
We thank Yue (Knox) Liu (@yueyueL) for responsibly disclosing this vulnerability to the mitmproxy team.
Timeline
- 2025-12-08: Received initial report.
- 2025-12-09: Verified report and confirmed receipt.
- 2026-01-02: Informed researcher that patch will be part of the next regular patch release.
- 2026-04-12: Published patch release and advisory.
Impact
In mitmproxy 12.2.1 and below, the builtin LDAP proxy authentication does not correctly sanitize the username when querying the LDAP server. This allows a malicious client to bypass authentication.
Only mitmproxy instances using the proxyauth option with LDAP are affected. This option is not enabled by default.
CVE-2026-40606 has a CVSS score of 4.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (12.2.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
The vulnerability has been fixed in mitmproxy 12.2.2 and above.
Frequently Asked Questions
- What is CVE-2026-40606? CVE-2026-40606 is a medium-severity security vulnerability in mitmproxy (pip), affecting versions <= 12.2.1. It is fixed in 12.2.2.
- How severe is CVE-2026-40606? CVE-2026-40606 has a CVSS score of 4.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mitmproxy are affected by CVE-2026-40606? mitmproxy (pip) versions <= 12.2.1 is affected.
- Is there a fix for CVE-2026-40606? Yes. CVE-2026-40606 is fixed in 12.2.2. Upgrade to this version or later.
- Is CVE-2026-40606 exploitable, and should I be worried? Whether CVE-2026-40606 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-40606 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-40606? Upgrade
mitmproxyto 12.2.2 or later.