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KaTeX's maxExpand bypassed by `\edef`

Moderate severity GitHub Reviewed Published Mar 24, 2024 in KaTeX/KaTeX • Updated Mar 25, 2024

Package

npm katex (npm)

Affected versions

>= 0.10.0-beta, < 0.16.10

Patched versions

0.16.10

Description

Impact

KaTeX users who render untrusted mathematical expressions could encounter malicious input using \edef that causes a near-infinite loop, despite setting maxExpand to avoid such loops. This can be used as an availability attack, where e.g. a client rendering another user's KaTeX input will be unable to use the site due to memory overflow, tying up the main thread, or stack overflow.

Patches

Upgrade to KaTeX v0.16.10 to remove this vulnerability.

Workarounds

Forbid inputs containing the substring "\\edef" before passing them to KaTeX.
(There is no easy workaround for the auto-render extension.)

Details

KaTeX supports an option named maxExpand which prevents infinitely recursive macros from consuming all available memory and/or triggering a stack overflow error. However, what counted as an "expansion" is a single macro expanding to any number of tokens. The expand-and-define TeX command \edef can be used to build up an exponential number of tokens using only a linear number of expansions according to this definition, e.g. by repeatedly doubling the previous definition. This has been corrected in KaTeX v0.16.10, where every expanded token in an \edef counts as an expansion.

For more information

If you have any questions or comments about this advisory:

References

@edemaine edemaine published to KaTeX/KaTeX Mar 24, 2024
Published to the GitHub Advisory Database Mar 25, 2024
Reviewed Mar 25, 2024
Published by the National Vulnerability Database Mar 25, 2024
Last updated Mar 25, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.043%
(10th percentile)

CVE ID

CVE-2024-28243

GHSA ID

GHSA-64fm-8hw2-v72w

Source code

Credits

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