PT-2026-41476 · Crates.Io · Kanidm

Published

2026-05-06

·

Updated

2026-05-06

CVSS v3.1

3.7

Low

VectorAV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Summary

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

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:
rust
// 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.

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.

Affected versions

All published kanidmd lib releases; the comparison is still variable-time on master at 1.10.0-dev

Fix

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Weakness Enumeration

CWE-208

Related Identifiers

GHSA-53HJ-R94P-8C8F

Affected Products

Kanidm