RUSTSEC-2023-0073: Infinite decoding loop through specially crafted payload

What to do

1. See which version you have: cargo tree -i candid (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p candid. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example candid = "0.9.10") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

The Candid library causes a Denial of Service while parsing a specially crafted payload with empty data type. For example, if the payload is record { * ; empty } and the canister interface expects record { * } then the rust candid decoder treats empty as an extra field required by the type. The problem with type empty is that the candid rust library wrongly categorizes empty as a recoverable error when skipping the field and thus causing an infinite decoding loop.

Canisters using affected versions of candid are exposed to denial of service by causing the decoding to run indefinitely until the canister traps due to reaching maximum instruction limit per execution round. Repeated exposure to the payload will result in degraded performance of the canister.

For asset canister users, dfx versions >= 0.14.4 to <= 0.15.2-beta.0 ships asset canister with an affected version of candid.

Unaffected

• Rust canisters using candid < 0.9.0 or >= 0.9.10
• Rust canister interfaces of type other than record { * }
• Motoko based canisters
• dfx (for asset canister) <= 0.14.3 or >= 0.15.2

References

• GitHub Security Advisory (GHSA-7787-p7x6-fq3j)
• dfinity/candid/pull/478
• Candid Library Reference
• Candid Specification
• Internet Computer Specification

References

• Package: crates.io/crates/candid
• Advisory: rustsec.org/advisories/RUSTSEC-2023-0073.html
• Web: github.com/dfinity/candid/pull/478

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.