CVE-2023-26485

/// Technical description

cmark-gfm is GitHub's fork of cmark, a CommonMark parsing and rendering library and program in C. A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service. This CVE covers quadratic complexity issues when parsing text which leads with either large numbers of `_` characters. This issue has been addressed in version 0.29.0.gfm.10. Users are advised to upgrade. Users unable to upgrade should validate that their input comes from trusted sources.

### Impact

A polynomial time complexity issue in cmark-gfm may lead to unbounded resource exhaustion and subsequent denial of service.

### Proof of concept

```

$ ~/cmark-gfm$ python3 -c 'pad = "_" * 100000; print(pad + "." + pad, end="")' | time ./build/src/cmark-gfm --to plaintext

```

Increasing the number 10000 in the above commands causes the running time to increase quadratically.

### Patches

This vulnerability have been patched in 0.29.0.gfm.10.

### Note on cmark and

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References