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Fencer Vulns
high 7.5

CVE-2023-6245 json

Infinite decoding loop through specially crafted payload

published 2023-12-08 2 y ago modified 2026-06-17 4 mo ago also GHSA-7787-p7x6-fq3j , RUSTSEC-2023-0073 , EUVD-2023-3140

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits
0
none known

Summary

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 the 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. Note: Canisters written in Motoko are unaffected.

Patch / fix

  • crates.io candid 0.9.10
  • Internet Computer Candid 0.9.10

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
23 mo ago

Exploit prediction

1.21% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
crates.io candid
>=0.9.0, <0.9.10
0.9.10

Affected products

  • Internet Computer Candid

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition
  • CWE-1288 Improper Validation of Consistency within Input
  • CWE-168 Improper Handling of Inconsistent Special Elements
  • CWE-20 Improper Input Validation
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.