Summary
ReDoS in LDAP schema parser
https://github.com/python-ldap/python-ldap/issues/424
Workarounds
As a workaround, users can check input for excessive amount of backslashes in schemas. More than a dozen backslashes per line are atypical.
References
For more information
If you have any questions or comments about this advisory:
- Open an issue in python-ldap tracker
Impact
The LDAP schema parser of python-ldap 3.3.1 and earlier are vulnerable to a regular expression denial-of-service attack. The issue affects clients that use ldap.schema package to parse LDAP schema definitions from an untrusted source.
A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.
GHSA-R8WQ-QRXC-HMCM has a CVSS score of 6.5 (Medium). The vector is network-reachable, low 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 (3.4.0); 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.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
The upcoming release of python-ldap 3.4.0 will contain a workaround to prevent ReDoS attacks. The schema parser refuses schema definitions with an excessive amount of backslashes.
Frequently Asked Questions
- What is GHSA-R8WQ-QRXC-HMCM? GHSA-R8WQ-QRXC-HMCM is a medium-severity inefficient regular expression (ReDoS) vulnerability in python-ldap (pip), affecting versions < 3.4.0. It is fixed in 3.4.0. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
- How severe is GHSA-R8WQ-QRXC-HMCM? GHSA-R8WQ-QRXC-HMCM has a CVSS score of 6.5 (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 python-ldap are affected by GHSA-R8WQ-QRXC-HMCM? python-ldap (pip) versions < 3.4.0 is affected.
- Is there a fix for GHSA-R8WQ-QRXC-HMCM? Yes. GHSA-R8WQ-QRXC-HMCM is fixed in 3.4.0. Upgrade to this version or later.
- Is GHSA-R8WQ-QRXC-HMCM exploitable, and should I be worried? Whether GHSA-R8WQ-QRXC-HMCM 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 GHSA-R8WQ-QRXC-HMCM 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 GHSA-R8WQ-QRXC-HMCM? Upgrade
python-ldapto 3.4.0 or later.