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Vulnerability record · CVE-2023-3138 · published 28 June 2023

CVE-2023-3138: X.org libx11 memory buffer overflow vulnerability

XX.Org · Libx11

A vulnerability was found in libX11. The security flaw occurs because the functions in src/InitExt.c in libX11 do not check that the values provided for the Request, Event, or Error IDs are within the bounds of the arrays that those functions write to, using those IDs as array indexes. They trust that they were called with values provided by an Xserver adhering to the bounds specified in the X11 protocol, as all X servers provided by X.Org do. As the protocol only specifies a single byte for these values, an out-of-bounds value provided by a malicious server (or a malicious proxy-in-the-middle) can only overwrite other portions of the Display structure and not write outside the bounds of the Display structure itself, possibly causing the client to crash with this memory corruption.

7.5 CVSS 3.1 High EPSS 1.7% · top 24.2% CWE-119 · Memory buffer overflowCWE-787 · Out-of-bounds write
7.5CVSS 3.1 base score
1.7%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
10References
17 Jun 2026Last modified by NVD

Description

A vulnerability was found in libX11. The security flaw occurs because the functions in src/InitExt.c in libX11 do not check that the values provided for the Request, Event, or Error IDs are within the bounds of the arrays that those functions write to, using those IDs as array indexes. They trust that they were called with values provided by an Xserver adhering to the bounds specified in the X11 protocol, as all X servers provided by X.Org do. As the protocol only specifies a single byte for these values, an out-of-bounds value provided by a malicious server (or a malicious proxy-in-the-middle) can only overwrite other portions of the Display structure and not write outside the bounds of the Display structure itself, possibly causing the client to crash with this memory corruption.

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

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://access.redhat.com/security/cve/CVE-2023-3138 Third Party Advisory
https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/304a654a0d57bf0f00d8998185f0360332cfa36c Patch
https://lists.x.org/archives/xorg-announce/2023-June/003406.html Mailing ListPatch
https://lists.x.org/archives/xorg-announce/2023-June/003407.html Mailing ListPatch
https://security.netapp.com/advisory/ntap-20231208-0008/
https://access.redhat.com/security/cve/CVE-2023-3138 Third Party Advisory
https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/304a654a0d57bf0f00d8998185f0360332cfa36c Patch
https://lists.x.org/archives/xorg-announce/2023-June/003406.html Mailing ListPatch
https://lists.x.org/archives/xorg-announce/2023-June/003407.html Mailing ListPatch
https://security.netapp.com/advisory/ntap-20231208-0008/

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Source: NIST National Vulnerability Database (record CVE-2023-3138), CISA KEV, FIRST EPSS (scores of 2026-10-03). This page is refreshed as NVD updates the record.