LookupCol.c in X.Org X through X11R7.7 and libX11 before 1.7.1 might allow remote…
Priority MEDIUM 55CWE-120Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 8 fixed, 1 without a fix
Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-120 and the CVSS impact.
Summary
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.
Why it matters now
EPSS 0.10353 95th percentileScored 2026-11-07
Public exploit Yes 3 exploit referencesTagged by NVD
Fix Partial Red Hat: 3 advisoriesRed Hat: 8 fixed, 1 without a fix
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
CPE configurations NVD · 3
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:x.org:libx11:*:*:*:*:*:*:*:* | before 1.7.1 | Vulnerable | x.org |
| cpe:2.3:o:x.org:x_window_system:*:*:*:*:*:*:*:* | up to x11r7.7 | Vulnerable | x.org |
| cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* | 33 | Vulnerable | Fedoraproject |
- cpe:2.3:a:x.org:libx11:*:*:*:*:*:*:*:* Versions before 1.7.1 Vulnerable ·x.org
- cpe:2.3:o:x.org:x_window_system:*:*:*:*:*:*:*:* Versions up to x11r7.7 Vulnerable ·x.org
- cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* Versions 33 Vulnerable ·Fedoraproject
Remediation
Red Hat 3 advisories
- RHSA-2021:4326 Released 2021-11-09 · Red Hat rating ModeratelibX11 security update
- Red Hat Enterprise Linux AppStream (v. 8) libX11-1.6.8-5.el8, libX11-common-1.6.8-5.el8, libX11-devel-1.6.8-5.el8 +1
- RHSA-2021:3477 Released 2021-09-09 · Red Hat rating ImportantRHV-H security update (redhat-virtualization-host) 4.3.18
- RHEL 7-based RHEV-H for RHEV 4 (build requirements) redhat-virtualization-host-4.3.18-20210903.0.el7_9, redhat-virtualization-host-image-update-4.3.18-20210903.0.el7_9
- Red Hat Virtualization 4 Hypervisor for RHEL 7 redhat-virtualization-host-4.3.18-20210903.0.el7_9, redhat-virtualization-host-image-update-4.3.18-20210903.0.el7_9
- RHSA-2021:3296 Released 2021-08-30 · Red Hat rating ImportantlibX11 security update
- Red Hat Enterprise Linux Client (v. 7) libX11-1.6.7-4.el7_9, libX11-common-1.6.7-4.el7_9, libX11-devel-1.6.7-4.el7_9
- Red Hat Enterprise Linux ComputeNode Optional (v. 7) libX11-devel-1.6.7-4.el7_9
- Red Hat Enterprise Linux Server (v. 7) libX11-1.6.7-4.el7_9, libX11-1.6.7-4.el7_9.ppc, libX11-common-1.6.7-4.el7_9 +2
- Red Hat Enterprise Linux Workstation (v. 7) libX11-1.6.7-4.el7_9, libX11-common-1.6.7-4.el7_9, libX11-devel-1.6.7-4.el7_9
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| RHEL 7-based RHEV-H for RHEV 4 (build requirements) | Fixed | RHSA-2021:3477 |
| Red Hat Ansible Tower 3.8 for RHEL 7 | Fixed | — |
| Red Hat Enterprise Linux AppStream (v. 8) | Fixed | RHSA-2021:4326 |
| Red Hat Enterprise Linux Client (v. 7) | Fixed | RHSA-2021:3296 |
| Red Hat Enterprise Linux ComputeNode Optional (v. 7) | Fixed | RHSA-2021:3296 |
| Red Hat Enterprise Linux Server (v. 7) | Fixed | RHSA-2021:3296 |
| Red Hat Enterprise Linux Workstation (v. 7) | Fixed | RHSA-2021:3296 |
| Red Hat Virtualization 4 Hypervisor for RHEL 7 | Fixed | RHSA-2021:3477 |
Not affected: 2 products
- RHEL 7-based RHEV-H for RHEV 4 (build requirements)
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2021-31535
- 2026-10-03 Alias added: GHSA-3vp2-rf63-rc8p
References
Exploit 3
Advisory 12
- https://lists.freedesktop.org/archives/xorg/
- [oss-security] 20210518 libX11 security advisory: May 18, 2021
- 20210520 CVE-2021-31535 libX11 Insufficient Length Checks PoC and Archeology
- [debian-lts-announce] 20210524 [SECURITY] [DLA 2666-1] libx11 security update
- DSA-4920
- 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://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/
- FEDORA-2021-62bb9998b2
Other 4
- [kafka-dev] 20210831 Security vulnerabilities in kafka:2.13-2.6.0/2.7.0 docker image
- [kafka-users] 20210831 Security vulnerabilities in kafka:2.13-2.6.0/2.7.0 docker image
- [kafka-users] 20210901 Re: [EXTERNAL] Re: Security vulnerabilities in kafka:2.13-2.6.0/2.7.0 docker image
- [kafka-dev] 20210901 Re: [EXTERNAL] Re: Security vulnerabilities in kafka:2.13-2.6.0/2.7.0 docker image
Sources
- CVE-2021-31535 · CVE Program
- CVE-2021-31535 · NVD
- FIRST EPSS
- GHSA-3vp2-rf63-rc8p · GitHub Advisory Database · CC BY 4.0
- CVE-2021-31535 · Red Hat security data · CC BY 4.0
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