CVE-2023-3138Network attack vector

Client crash via unchecked extension ID indexes

Published Jun 28, 2023 · Updated Aug 2, 2024

Out-of-bounds writes in X.Org libX11 before 1.8.6 allow remote attackers to crash X11 clients through malicious server replies. The InitExt.c functions use unvalidated one-byte Request, Event, and Error IDs as indexes into arrays within the Display structure. Exploitation requires a client to connect to an attacker-controlled X server or receive replies altered by a man-in-the-middle attacker; testing established a client crash, not writes beyond the Display structure.

CVSS severity7.5
High
EPSS probability1.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds writes in X.Org libX11 before 1.8.6 allow remote attackers to crash X11 clients through malicious server replies. The InitExt.c functions use unvalidated one-byte Request, Event, and Error IDs as indexes into arrays within the Display structure. Exploitation requires a client to connect to an attacker-controlled X server or receive replies altered by a man-in-the-middle attacker; testing established a client crash, not writes beyond the Display structure.

The record

CVE
CVE-2023-3138
Published
Jun 28, 2023
Updated
Aug 2, 2024
Vendor
X.Org
Product
libX11
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 28, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=libX11 1.8.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

X.Org · libX11version=libX11 1.8.6

Published CVSS scores

6.5Amazon LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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