cmark-gfm is GitHubs fork of cmark, a CommonMark parsing and rendering library and program in C. In versions prior to 0.29.0.gfm.6 a polynomial time complexity issue in cmark-gfms autolink extension may lead to unbounded resource exhaustion and subsequent denial of service. Users may verify the patch by running python3 -c print(![l* 100000 + n) | ./cmark-gfm -e autolink, which will resource exhaust on unpatched cmark-gfm but render correctly on patched cmark-gfm. This vulnerability has been patched in 0.29.0.gfm.6. Users are advised to upgrade. Users unable to upgrade should disable the use of the autolink extension.
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Cmark-gfm | Github | * | 0.29.0.gfm.6 (excluding) |
| Cmark-gfm | Ubuntu | esm-apps/focal | * |
| Cmark-gfm | Ubuntu | esm-apps/jammy | * |
| Cmark-gfm | Ubuntu | focal | * |
| Cmark-gfm | Ubuntu | jammy | * |
| Cmark-gfm | Ubuntu | kinetic | * |
| Cmark-gfm | Ubuntu | lunar | * |
| Cmark-gfm | Ubuntu | mantic | * |
| Cmark-gfm | Ubuntu | trusty | * |
| Cmark-gfm | Ubuntu | upstream | * |
| Cmark-gfm | Ubuntu | xenial | * |
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.