CVE-2023-6245 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in candid. A fix is available for candid — see the affected versions and patch details below.
Candid infinite decoding loop through specially crafted payload
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-6245.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
candidReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Impact
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
< 0.9.0or>= 0.9.10 - Rust canister interfaces of type other than
record { * } - Motoko based canisters
- dfx (for asset canister)
<= 0.14.3or>= 0.15.2
Patches
The issue has been patched in 0.9.10. All rust based canisters on candid versions >= 0.9.0 must upgrade their candid versions to >= 0.9.10 and deploy their canisters to mainnet as soon as possible.
Workarounds
There is no workaround for canisters using the affected versions of candid other than upgrading to patched version.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | candid | ≥ 0.9.0&&< 0.9.10 | 0.9.10cargo update -p candid --precise 0.9.10 |
Affected Products
candiddfinityDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for candid, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update candid to 0.9.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-6245 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2023-6245 in your dependencies?
Find it across crates.io, including transitive dependencies.