CVE-2021-31535

CRITICAL
9.8
CVSS Score
Published: May 27, 2021 at 12:26 PM UTC
Updated: June 17, 2026 at 03:51 AM UTC
3 products affected across 2 vendorsFedoraLIBX11X Window System

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Severity
CRITICAL9.8
Exploit prediction
EPSS 11%

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 1.7.1
Affected range stops below 1.7.1, so it looks safe — our inference, not a vendor statement
v ≤ x11r7.7

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-120

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