fix(msgpack): Recursion limit#6212
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The msgpack attachment path (extract_attached_event) deserializes an Event with rmp_serde, which enforces no recursion limit (unlike serde_json's 128-level cap). A ~200 KB payload of nested arrays, well under the 1 MiB max_event_size, drives Value deserialization ~200k frames deep and overflows the stack. The proof re-execs the test binary in a child process and asserts it is killed by a stack overflow, since the overflow aborts the process and cannot be caught in-thread. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
rmp_serde enforces a recursion limit, but its default (1024) is too high for Relay's deeply generic types such as Annotated<Value>: each recursive deserialization frame is several KB, so a maliciously nested msgpack payload exhausts the thread stack and aborts the process well before the built-in counter trips. The max_event_size check (1 MiB) does not help, since nesting depth is unbounded far below the byte limit. Cap nesting at 128 (the same depth serde_json enforces by default) on all user-facing msgpack deserialization paths: attached events, msgpack breadcrumbs, replay video events, and event-id extraction. Deeply nested payloads are now rejected with an error instead of crashing. Invert the proof-of-vulnerability test into a regression test that asserts graceful rejection. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
jjbayer
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Jul 10, 2026
Co-authored-by: Joris Bayer <jjbayer@gmail.com>
Dav1dde
approved these changes
Jul 10, 2026
| let payload = item.payload(); | ||
| let mut deserializer = rmp_serde::Deserializer::new(payload.as_ref()); | ||
| // rmp_serde's default limit (1024) is too high for our types. | ||
| deserializer.set_max_depth(crate::utils::MSGPACK_MAX_DEPTH); |
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We could make a function in the utils which must be used to construct the Deserializer which will also always have the limit applied.
Then we can put rmp_serde on the shit list.
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Impose a recursion limit of 128 on message pack deserialization.
Closes INGEST-990.