What is the CVSS score of CVE-2021-31535?

CVE-2021-31535 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 10.6%.

Is there a public PoC exploit available for CVE-2021-31535?

Yes, a public proof-of-concept exploit is available for CVE-2021-31535. Prioritise patching immediately. EPSS: 10.6%.

Libx11 CVE-2021-31535

CRITICAL

Classic Buffer Overflow (CWE-120)

2021-05-27 cve@mitre.org

Buffer Overflow RCE Libx11 X Window System Fedora

9.8

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

9.8 CRITICAL

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

CVE Published

May 27, 2021 - 13:15 nvd

CRITICAL 9.8

DescriptionNVD

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.

AnalysisAI

LookupCol.c in X.Org X through X11R7.7 and libX11 before 1.7.1 might allow remote attackers to execute arbitrary code. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

Technical ContextAI

This vulnerability is classified as Buffer Copy without Size Check (CWE-120), which allows attackers to overflow a buffer to corrupt adjacent memory. 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 products include: X.Org Libx11, X.Org X Window System, Fedoraproject Fedora. Version information: before 1.7.1.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Always validate buffer sizes before copy operations. Use bounded functions (strncpy, snprintf). Enable compiler protections.