HOME VULNERABILITIESCVE-2021-31535

CRITICAL

CVE-2021-31535

CWE-120Published: May 27, 2021· Updated: Jun 17, 2026

9.8

CVSS v3.1

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.

Technical Analysis

CVE-2021-31535 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges Req.None

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

Fedora1 product(s)

fedora

x.org2 product(s)

libx11x window system

Source: NVD CPE · 3 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time

Offensive Security exploit database

GitHub PoC Search

Community PoC repositories

Rapid7 / Metasploit

Metasploit module search

Security advisories & exploits

Official NIST entry

CVE Program entry

External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttp://packetstormsecurity.com/files/162737/libX11-Insufficient-Length-Check-Injection.html

ADVISORYhttp://seclists.org/fulldisclosure/2021/May/52

ADVISORYhttp://www.openwall.com/lists/oss-security/2021/05/18/2

ADVISORYhttps://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/8d2e02ae650f00c4a53deb625211a0527126c605

ADVISORYhttps://lists.debian.org/debian-lts-announce/2021/05/msg00021.html

ADVISORYhttps://lists.freedesktop.org/archives/xorg/

ADVISORYhttps://lists.x.org/archives/xorg-announce/2021-May/003088.html

ADVISORYhttps://security.gentoo.org/glsa/202105-16

ADVISORYhttps://security.netapp.com/advisory/ntap-20210813-0001/

ADVISORYhttps://unparalleled.eu/blog/2021/20210518-using-xterm-to-navigate-the-huge-color-space/

ADVISORYhttps://unparalleled.eu/publications/2021/advisory-unpar-2021-1.txt

ADVISORYhttps://www.debian.org/security/2021/dsa-4920

ADVISORYhttps://www.openwall.com/lists/oss-security/2021/05/18/2

ADVISORYhttps://www.openwall.com/lists/oss-security/2021/05/18/3

ADVISORYhttp://packetstormsecurity.com/files/162737/libX11-Insufficient-Length-Check-Injection.html

ADVISORYhttp://seclists.org/fulldisclosure/2021/May/52

ADVISORYhttp://www.openwall.com/lists/oss-security/2021/05/18/2

ADVISORYhttps://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/8d2e02ae650f00c4a53deb625211a0527126c605

ADVISORYhttps://lists.debian.org/debian-lts-announce/2021/05/msg00021.html

ADVISORYhttps://lists.freedesktop.org/archives/xorg/

ADVISORYhttps://lists.x.org/archives/xorg-announce/2021-May/003088.html

ADVISORYhttps://security.gentoo.org/glsa/202105-16

ADVISORYhttps://security.netapp.com/advisory/ntap-20210813-0001/

ADVISORYhttps://unparalleled.eu/blog/2021/20210518-using-xterm-to-navigate-the-huge-color-space/

ADVISORYhttps://unparalleled.eu/publications/2021/advisory-unpar-2021-1.txt

ADVISORYhttps://www.debian.org/security/2021/dsa-4920

ADVISORYhttps://www.openwall.com/lists/oss-security/2021/05/18/2

ADVISORYhttps://www.openwall.com/lists/oss-security/2021/05/18/3

All References (38)

→

http://packetstormsecurity.com/files/162737/libX11-Insufficient-Length-Check-Injection.htmlExploit · Third Party Advisory · VDB Entry

→

http://seclists.org/fulldisclosure/2021/May/52Mailing List · Third Party Advisory

→

http://www.openwall.com/lists/oss-security/2021/05/18/2Mailing List · Third Party Advisory

→

https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/8d2e02ae650f00c4a53deb625211a0527126c605Third Party Advisory

→

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%3Cdev.kafka.apache.org%3E

→

https://lists.apache.org/thread.html/rbf4ce74b0d1fa9810dec50ba3ace0caeea677af7c27a97111c06ccb7%40%3Cusers.kafka.apache.org%3E

→

https://lists.debian.org/debian-lts-announce/2021/05/msg00021.htmlThird Party Advisory

→

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TEOT4RLB76RVPJQKGGTIKTBIOLHX2NR6/

→

https://lists.freedesktop.org/archives/xorg/Third Party Advisory

→

https://lists.x.org/archives/xorg-announce/2021-May/003088.htmlVendor Advisory

→

https://security.gentoo.org/glsa/202105-16Third Party Advisory

→

https://security.netapp.com/advisory/ntap-20210813-0001/Third Party Advisory

→

https://unparalleled.eu/blog/2021/20210518-using-xterm-to-navigate-the-huge-color-space/Exploit · Third Party Advisory

Quick Facts

CVE IDCVE-2021-31535

CVSS Score9.8 / 10

SeverityCRITICAL

WeaknessCWE-120

CISA KEVNo

Affected2 vendor(s)

PublishedMay 27, 2021

Related CVEs (CWE-120)

Recommended Actions

→Apply vendor patches immediately
→Monitor CVE-2021-31535 in threat intel feeds
→Review IDS/IPS signatures for exploitation attempts

Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.

← All Vulnerabilities·Search for CVE-2021-31535·NVD