GHSA-r5fr-9gmv-jggh

Summary

A single unauthenticated GET to any /scim/v1/... endpoint with a ?filter= query string of a few thousand nested parentheses (≈ 4–12 KB) drives the recursive-descent PEG parser past the worker thread's stack guard page. Rust responds to stack overflow with std::process::abort() — the entire kanidmd process exits. The parse runs inside axum's Query<ScimEntryGetQuery> extractor, before any handler body and therefore before any ACL check.

Details

The SCIM filter grammar recurses on ( and not ( with no depth bound.

proto/src/scim_v1/mod.rs:263-433 — peg::parser! { grammar scimfilter() ... }:

// line 281
"not" separator()+ "(" e:parse() ")" { ScimFilter::Not(Box::new(e)) }
// line 293
"(" e:parse() ")" { e }

Both rules re-enter parse() without a depth counter.

proto/src/scim_v1/mod.rs:442-447 — impl FromStr for ScimFilter calls scimfilter::parse(input) directly on the raw string with no length or depth pre-check.

proto/src/scim_v1/mod.rs:80-81 — ScimEntryGetQuery.filter is #[serde_as(as = "Option<DisplayFromStr>")], so deserialising the query struct invokes ScimFilter::from_str on attacker bytes.

Unauthenticated reachability — nine handlers in server/core/src/https/v1_scim.rs (route table at lines 865-1029) take Query<ScimEntryGetQuery> as an argument: /scim/v1/Entry, /scim/v1/Entry/{id}, /scim/v1/Person/{id}, /scim/v1/Application, /scim/v1/Application/{id}, /scim/v1/Class, /scim/v1/Attribute, /scim/v1/Message, /scim/v1/Message/{id}. The SCIM router is merged unconditionally for every server role (server/core/src/https/mod.rs:312).

Axum extracts handler arguments before the handler body runs. The preceding VerifiedClientInformation extractor (server/core/src/https/extractors/mod.rs:16-91) always returns Ok (line 89) regardless of credentials; authorization is deferred to the handler body, which is never reached.

The existing semantic depth limit...