CVE-2021-31535

Libx11 vulnerability

CVSS

9.8

EPSS

10.6%

EPSS pct

95th

Exploited

No known

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 vendor

X.Org

Affected product

Libx11

CVSS vector

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

Weakness type (CWE)

CWE-120 — Classic Buffer Overflow

Published

2021-05-27

Risk analysis

Based on its CVSS vector, this vulnerability is exploitable over the network, low attack complexity, requiring no privileges, no user interaction. Successful exploitation leads to high impact to confidentiality, high impact to integrity, high impact to availability.

Its EPSS score of 10.6% reflects a moderate probability of exploitation activity in the wild over the next 30 days, placing it above 95% of all scored CVEs.

Check your external exposure to CVE-2021-31535

Confirm whether X.Org Libx11 is running on any internet-facing host or subdomain.
Match discovered service fingerprints against the version affected by CVE-2021-31535.
Prioritise remediation if the asset is public, business-critical, or near authentication/payment flows.

How ThreatPort helps with CVE-2021-31535

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