GHSA-53hj-r94p-8c8f: Kanidm Kanidm Has Non-constant-time Comparison Of Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-53hj-r94p-8c8f",
  "modified" : "2026-05-06T23:37:56Z",
  "published" : "2026-05-06T23:37:56Z",
  "aliases" : [ ],
  "summary" : "Kanidm has non-constant-time comparison of OAuth2 client_secret",
  "details" : "### Summary\n\nThe 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.\n\n### Details\n\n- https://github.com/kanidm/kanidm/blob/master/server/lib/src/idm/oauth2.rs#L1135 — variable-time comparison in `check_oauth2_token_exchange`\n- https://cwe.mitre.org/data/definitions/208.html — CWE-208: Observable Timing Discrepancy\n\n### PoC\n\nStatic 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:\n\n```rust\n// server/lib/src/idm/oauth2.rs:1135  (check_oauth2_token_exchange)\nif authz_secret == &secret { … } else { return Err(Oauth2Error::AuthenticationRequired); }\n```\n\n`String: PartialEq` delegates to `<[u8] as PartialEq>::eq`, which checks length equality then iterates byte-by-byte and returns on the first difference.\n\n### Impact\n\nAn 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.\n\n### Affected versions\n\nAll published `kanidmd_lib` releases; the comparison is still variable-time on `master` at 1.10.0-dev",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "kanidm"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.9.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.9.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/kanidm/kanidm/security/advisories/GHSA-53hj-r94p-8c8f"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/kanidm/kanidm"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-208" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T23:37:56Z",
    "nvd_published_at" : null
  }
}