CVE-2026-55999Network attack vector

Code execution via undersized glamor glyph slots

Published Jul 8, 2026 · Updated Jul 8, 2026

Heap buffer overflow in X.Org Server before 21.1.24 and Xwayland before 24.1.13 allows local users to execute code in the server process. glamor_font_get allocates atlas slots from a font's declared maxbounds, then copies glyph bitmaps using unchecked per-glyph dimensions. Exploitation requires an authenticated X client, a crafted PCF font, and a glamor-backed drawable; the overflow has attacker-controlled content and extent.

CVSS severity8.5
High
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in X.Org Server before 21.1.24 and Xwayland before 24.1.13 allows local users to execute code in the server process. glamor_font_get allocates atlas slots from a font's declared maxbounds, then copies glyph bitmaps using unchecked per-glyph dimensions. Exploitation requires an authenticated X client, a crafted PCF font, and a glamor-backed drawable; the overflow has attacker-controlled content and extent.

The record

CVE
CVE-2026-55999
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
X.Org
Product
X.Org Server
Classifications
CWE-805, CWE-122
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 2026Record 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=0 <21.1.24

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

X.Org · X.Org Serverversion=0 <21.1.24
X.Org · Xwaylandversion=0 <24.1.13

Published CVSS scores

7.5Red HatCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
8.5SUSECVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
7.5Oracle LinuxCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-805Buffer Access with Incorrect Length Value
CWE-122Heap-based Buffer Overflow

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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