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Critical libXfont Vulnerabilities Lead to Denial of Service Risks

Critical libXfont Vulnerabilities Lead to Denial of Service Risks

First seen 20 Jul 2026, 17:39 UTC

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ThreatCluster AI
ThreatCluster July 21, 2026 at 16:29 UTC

Multiple vulnerabilities were discovered in libXfont, affecting the X server. These include heap buffer overflows due to improper handling of bitmap fonts and glyph bounds, allowing attackers to crash the service or execute arbitrary code. The vulnerabilities are identified as CVE-2026-56001, CVE-2026-56002, and CVE-2026-56003, all published on 2026-07-08. An attacker with access to the X server can exploit these vulnerabilities, leading to potential denial of service. The affected systems include various Ubuntu LTS versions, with patches available for users. Security updates are recommended to mitigate these risks. The vulnerabilities have been confirmed and reported by both Ubuntu and Linuxsecurity.

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Timeline

2017-12-01
CVE-2017-16611 published
Vulnerability assigned a CVE identifier and published in the National Vulnerability Database.
MITRE
2026-07-08
CVE-2026-56001 published
Heap buffer overflow in libXfont due to improper handling of bitmap fonts allows potential code execution.
Ubuntu
2026-07-08
CVE-2026-56002 published
Improper glyph bounds checking in libXfont can lead to denial of service for authenticated X clients.
Ubuntu
2026-07-08
CVE-2026-56003 published
Buffer size mismanagement in libXfont parsing PCF fonts leads to heap buffer overflow vulnerabilities.
Ubuntu
2026-07-20
Security advisory published
Ubuntu and Linuxsecurity issued advisories detailing the vulnerabilities and recommended patches.
Linuxsecurity

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