USN-8560-1: libXfont vulnerabilities
It was discovered that libXfont incorrectly handled scaling bitmap fonts, leading to a heap buffer overflow. An attacker able to access the X server could use this issue to cause libXfont to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-56001) It was discovered that libXfont did not properly check glyph bounds when reading PCF fonts, leading to a heap buffer overflow. An authenticated X client could use this issue to cause libXfont to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-56002) It was discovered that libXfont did not properly check the size of the property buffer when parsing PCF fonts, leading to a heap buffer overflow. An authenticated X client could use this issue to cause libXfont to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-56003)
CSIRTS triage
- What
- libXfont has vulnerabilities that could lead to denial of service or arbitrary code execution.
- Who is affected
- Authenticated X clients accessing the X server.
- Urgency
- Remediation is urgent due to the potential for exploitation and the severity of the vulnerabilities.
- Action
- Users should apply the necessary updates to libXfont.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://ubuntu.com/security/notices/USN-8560-1
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-560010.38% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 31% of all scored CVEs.
- Low exploitation riskCVE-2026-560020.43% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 35% of all scored CVEs.
- Low exploitation riskCVE-2026-560030.37% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 30% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-56001 | coverage & exploitation status | NVD · CVE.org |
| CVE-2026-56002 | coverage & exploitation status | NVD · CVE.org |
| CVE-2026-56003 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.
- medium[NEW] [medium] X.Org X11 Server (libXfont2): Multiple vulnerabilities allow execution of arbitrary code with a…cert-bund
- unknownMultiple vulnerabilities in Microsoft Azure Linux (July 15, 2026)cert-fr-avis
- unknownDSA-6388-1 libxfont - security updatedebian
- highCVE-2026-56001: libXfont2 BitmapScaleBitmaps Integer Overflow Heap Buffer Overflowmsrc
- highCVE-2026-56002: libXfont2 PCF Font Parsing Heap Buffer Overflowmsrc
- highCVE-2026-56003: libXfont2 computeProps Property Buffer Heap Buffer Overflowmsrc
- highCVE-2026-56003: A heap buffer overflow due to missing size checking in the property buffer when parsing PCF fi…nvd
- highCVE-2026-56002: A heap bufferflow in pcfReadFont() due to missing glyph bounds checking in libXfont2 before 2.…nvd
- highCVE-2026-56001: A heap buffer overflow in BitmapScaleBitmaps in libXfont2 before 2.0.8 due to an overflowing 3…nvd
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