Integer overflow in cmark-gfm table parsing extension leads to heap memory corruption

Impact

CommonMarker uses cmark-gfm for rendering
Github Flavored Markdown.
An integer overflow in cmark-gfm’s table row parsing
may lead to heap memory corruption when parsing tables who’s marker
rows contain more than UINT16_MAX columns. The impact of this heap
corruption ranges from Information Leak to Arbitrary Code Execution.

If affected versions of CommonMarker are used for rendering remote
user controlled markdown, this vulnerability may lead to
Remote Code Execution (RCE).

Patches

This vulnerability has been patched in the following CommonMarker release:

• v0.23.4

Workarounds

The vulnerability exists in the table markdown extensions of
cmark-gfm. Disabling any use of the table extension will prevent
this vulnerability from being triggered.

References

• https://github.com/github/cmark-gfm/security/advisories/GHSA-mc3g-88wq-6f4x

Acknowledgements

We would like to thank Felix Wilhelm of Google’s Project Zero
for reporting this vulnerability

For more information

If you have any questions or comments about this advisory:

• Open an issue in CommonMarker