Summary
Kanidm has non-constant-time comparison of OAuth2 client_secret
The kanidmd OAuth2 token-exchange (/oauth2/token) and token-introspection (/oauth2/token/introspect) endpoints compare the supplied client_secret against the stored secret using Rust's PartialEq on String, which short-circuits on the first mismatching byte. This produces an observable timing discrepancy that varies with the length of the matching prefix.
Details
- https://github.com/kanidm/kanidm/blob/master/server/lib/src/idm/oauth2.rs#L1135, variable-time comparison in
check_oauth2_token_exchange - https://cwe.mitre.org/data/definitions/208.html, CWE-208: Observable Timing Discrepancy
PoC
Static analysis only, no timing-recovery script was run because remote recovery of a 48-byte high-entropy secret over HTTPS is not practically demonstrable. The variable-time behaviour is established by inspection:
// server/lib/src/idm/oauth2.rs:1135 (check_oauth2_token_exchange)
if authz_secret == &secret { … } else { return Err(Oauth2Error::AuthenticationRequired); }
String: PartialEq delegates to <[u8] as PartialEq>::eq, which checks length equality then iterates byte-by-byte and returns on the first difference.
Affected versions
All published kanidmd_lib releases; the comparison is still variable-time on master at 1.10.0-dev
Impact
An unauthenticated network attacker who can reach the OAuth2 endpoints can submit arbitrary client_id/client_secret pairs and observe response latency. In principle the early-exit comparison leaks the position of the first mismatching byte, providing a timing oracle toward incremental recovery of a confidential client's secret. In practice the stored secret is a server-generated 48-character high-entropy string, the comparison runs inside an async tokio handler behind TLS, and network jitter is orders of magnitude larger than a single byte-compare, so remote recovery is not considered realistic with current techniques. This is a hardening issue rather than a practically exploitable vulnerability.
GHSA-53HJ-R94P-8C8F has a CVSS score of 3.7 (Low). 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 (1.9.3); 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.
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Frequently Asked Questions
- What is GHSA-53HJ-R94P-8C8F? GHSA-53HJ-R94P-8C8F is a low-severity security vulnerability in kanidm (rust), affecting versions <= 1.9.2. It is fixed in 1.9.3.
- How severe is GHSA-53HJ-R94P-8C8F? GHSA-53HJ-R94P-8C8F has a CVSS score of 3.7 (Low). 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 kanidm are affected by GHSA-53HJ-R94P-8C8F? kanidm (rust) versions <= 1.9.2 is affected.
- Is there a fix for GHSA-53HJ-R94P-8C8F? Yes. GHSA-53HJ-R94P-8C8F is fixed in 1.9.3. Upgrade to this version or later.
- Is GHSA-53HJ-R94P-8C8F exploitable, and should I be worried? Whether GHSA-53HJ-R94P-8C8F 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-53HJ-R94P-8C8F 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-53HJ-R94P-8C8F? Upgrade
kanidmto 1.9.3 or later.