# CVE-2021-31535: Code injection in n/a

> Remote attackers can execute arbitrary code or bypass authorization by sending oversized color lookup requests to the X server via the libX11 library.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 May 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-31535, ALSA-2021:4326, DEBIAN-CVE-2021-31535, DLA-2666-1, DSA-4920-1, GHSA-3vp2-rf63-rc8p, JLSEC-2026-471, MGASA-2021-0219, OESA-2021-1235, RHSA-2021:3296, RHSA-2021:4326, RLSA-2021:4326, SUSE-SU-2021:14748-1, SUSE-SU-2021:1765-1, SUSE-SU-2021:1766-1, SUSE-SU-2021:1892-1, SUSE-SU-2021:1897-1, UBUNTU-CVE-2021-31535, USN-4966-1, USN-4966-2, openSUSE-SU-2021:0807-1, openSUSE-SU-2021:0857-1, openSUSE-SU-2021:1897-1

## What is CVE-2021-31535?

CVE-2021-31535 is a critical code injection vulnerability in Fedoraproject Fedora, published on 27 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2021-31535?

It affects 3 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `libX11` | AlmaLinux:8 | All versions | 1.6.8-5.el8 |
| `libX11-common` | AlmaLinux:8 | All versions | 1.6.8-5.el8 |
| `libX11-devel` | AlmaLinux:8 | All versions | 1.6.8-5.el8 |
| `libX11-xcb` | AlmaLinux:8 | All versions | 1.6.8-5.el8 |
| `libX11` | Red Hat:enterprise_linux:7::client | All versions | 0:1.6.7-4.el7_9 |
| `libX11-common` | Red Hat:enterprise_linux:7::client | All versions | 0:1.6.7-4.el7_9 |
| `libX11-debuginfo` | Red Hat:enterprise_linux:7::client | All versions | 0:1.6.7-4.el7_9 |
| `libX11-devel` | Red Hat:enterprise_linux:7::client | All versions | 0:1.6.7-4.el7_9 |
| `libX11-debuginfo` | Red Hat:enterprise_linux:7::computenode | All versions | 0:1.6.7-4.el7_9 |
| `libX11-devel` | Red Hat:enterprise_linux:7::computenode | All versions | 0:1.6.7-4.el7_9 |
| `libX11` | Red Hat:enterprise_linux:7::server | All versions | 0:1.6.7-4.el7_9 |
| `libX11-common` | Red Hat:enterprise_linux:7::server | All versions | 0:1.6.7-4.el7_9 |
| `libX11-debuginfo` | Red Hat:enterprise_linux:7::server | All versions | 0:1.6.7-4.el7_9 |
| `libX11-devel` | Red Hat:enterprise_linux:7::server | All versions | 0:1.6.7-4.el7_9 |
| `libX11` | Red Hat:enterprise_linux:7::workstation | All versions | 0:1.6.7-4.el7_9 |
| `libX11-common` | Red Hat:enterprise_linux:7::workstation | All versions | 0:1.6.7-4.el7_9 |
| `libX11-debuginfo` | Red Hat:enterprise_linux:7::workstation | All versions | 0:1.6.7-4.el7_9 |
| `libX11-devel` | Red Hat:enterprise_linux:7::workstation | All versions | 0:1.6.7-4.el7_9 |
| `libX11` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11-common` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11-debugsource` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11-devel` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11-xcb` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11-xcb-debuginfo` | Red Hat:enterprise_linux:8::appstream | All versions | 0:1.6.8-5.el8 |
| `libX11` | Rocky Linux:8 | All versions | 0:1.6.8-5.el8 |
| `libX11` | SUSE:Enterprise Storage 6 | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:HPE Helion OpenStack 8 | All versions | 1.6.2-12.21.1 |
| `libX11` | SUSE:Linux Enterprise High Performance Computing 15 SP1-ESPOS | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:Linux Enterprise High Performance Computing 15 SP1-LTSS | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:Linux Enterprise High Performance Computing 15-ESPOS | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:Linux Enterprise High Performance Computing 15-LTSS | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:Linux Enterprise Micro 5.0 | All versions | 1.6.5-3.18.1 |
| `libX11` | SUSE:Linux Enterprise Micro 5.0 | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:Linux Enterprise Module for Basesystem 15 SP2 | All versions | 1.6.5-3.18.1 |
| `libX11` | SUSE:Linux Enterprise Module for Basesystem 15 SP2 | All versions | 1.6.5-3.21.1 |
| `libX11` | SUSE:Linux Enterprise Module for Basesystem 15 SP3 | All versions | 1.6.5-3.18.1 |
| `libX11` | SUSE:Linux Enterprise Module for Basesystem 15 SP3 | All versions | 1.6.5-3.21.1 |
| `xorg-x11-libX11` | SUSE:Linux Enterprise Point of Sale 11 SP3 | All versions | 7.4-5.11.72.27.1 |
| `xorg-x11-libX11` | SUSE:Linux Enterprise Server 11 SP4-LTSS | All versions | 7.4-5.11.72.27.1 |

Products: Fedoraproject Fedora, X.org Libx11, X.org X Window System.

## How do I fix CVE-2021-31535?

Upgrade to a fixed version.

## Is CVE-2021-31535 being exploited?

There is no known exploitation of CVE-2021-31535 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31535 and fix it if it is affected.

What it is: CVE-2021-31535 is a critical code injection vulnerability in Fedoraproject Fedora, published on 27 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-31535 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-31535/ (Markdown: https://insights.sbomify.com/CVE-2021-31535/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31535
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31535
- OSV: https://osv.dev/vulnerability/CVE-2021-31535

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31535/
Summaries are generated and may contain mistakes; the official description above is the record.