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Quadratic complexity bugs may lead to a denial of service

Moderate
anticomputer published GHSA-66g8-4hjf-77xh Mar 31, 2023

Package

cmark-gfm

Affected versions

<= 0.29.0.gfm.9

Patched versions

0.29.0.gfm.10

Description

Impact

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

Proof of concept

Issue 1:

python3 -c 'n = 10000; print(">"*n + "a*"*n)' | cmark-gfm

Issue 2:

python3 -c 'n = 10000; print(" -" * n + "x" + "\n" * n)' | cmark-gfm

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

Patches

These vulnerabilities have been patched in 0.29.0.gfm.10.

Note on cmark and cmark-gfm

cmark-gfm is a fork of cmark that adds the GitHub Flavored Markdown extensions. The two codebases have diverged over time, but share a common core. These bugs affect both cmark and cmark-gfm.

Credit

We would like to thank @nwellnhof for reporting the first vulnerability (issue 1). Issue 2 was subsequently found by GitHub Security Lab.

References

https://en.wikipedia.org/wiki/Time_complexity

For more information

If you have any questions or comments about this advisory:

Severity

Moderate

CVE ID

CVE-2023-24824

Weaknesses

Credits