# CVE-2023-6245: Infinite decoding loop through specially crafted payload

> Attackers can cause a denial of service in Internet Computer canisters by sending crafted payloads that trigger an infinite decoding loop in the Candid library.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Dec 2023
- **Updated:** 2 Dec 2024
- **Also known as:** GHSA-7787-p7x6-fq3j, RUSTSEC-2023-0073

## What is CVE-2023-6245?

CVE-2023-6245 is a high-severity denial of service vulnerability in Internet Computer Candid, published on 8 Dec 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-20 (Improper Input Validation), CWE-835 (Loop with Unreachable Exit Condition), CWE-168 (Improper Handling of Inconsistent Special Elements), CWE-1288 (Improper Validation of Consistency within Input)

## Which versions are affected by CVE-2023-6245?

3 open source packages ship an affected version, including candid. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `candid` | crates.io | From 0.9.0 | 0.9.10 |
| `candid` | crates.io | From 0.9.0 | 0.9.10 |
| `candid` | crates.io | From 0.9.0 | 0.9.10 |

Products: Dfinity Candid.

## How do I fix CVE-2023-6245?

Upgrade candid to 0.9.10 or later.

## Is CVE-2023-6245 being exploited?

There is no known exploitation of CVE-2023-6245 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-6245 and fix it if it is affected.

What it is: CVE-2023-6245 is a high-severity denial of service vulnerability in Internet Computer Candid, published on 8 Dec 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-6245 in the wild and no public exploit code.

Affected packages and fixed versions:
- candid (crates.io): affected from 0.9.0; fixed in 0.9.10
- candid (crates.io): affected from 0.9.0; fixed in 0.9.10
- candid (crates.io): affected from 0.9.0; fixed in 0.9.10

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-6245/ (Markdown: https://insights.sbomify.com/CVE-2023-6245/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-6245
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-6245
- OSV: https://osv.dev/vulnerability/CVE-2023-6245

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-6245/
Summaries are generated and may contain mistakes; the official description above is the record.