CVE-2026-34085
Fontconfig Project Fontconfig 2.17.0
Raw vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:LSummary
CVE-2026-34085 is a medium-severity Off-by-one Error (CWE-193) vulnerability in Fontconfig Project Fontconfig. Its CVSS base score is 5.9 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-34085 is an off-by-one error in memory allocation during SFNT capability handling in the fontconfig library versions prior to 2.17.1. The issue resides in the FcFontCapabilities function within fcfreetype.c, where it triggers a one-byte out-of-bounds write. This vulnerability, classified under CWE-193 (Off-by-one Error), carries a CVSS v3.1 base score of 5.9 (AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L) and could lead to application crashes or potential remote code execution depending on exploitation context.
A local attacker can exploit this vulnerability with low complexity and no privileges or user interaction required, as it only demands local access to the system. Successful exploitation results in low-impact confidentiality, integrity, and availability effects, such as limited data exposure, minor tampering, or denial of service via crashes, with the out-of-bounds write potentially enabling more severe outcomes like code execution in vulnerable font processing scenarios.
Mitigation is addressed in fontconfig version 2.17.1, with patches detailed in the project's GitLab repository, including commit b9bec06d73340f1b5727302d13ac3df307b7febc, merge request 446, and work item 481. Security practitioners should update to the fixed version and audit systems using affected fontconfig releases for local attack surface exposure.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-15934
Vulnerability Data
fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a one-byte out-of-bounds write, and potentially a crash or code execution. This is in FcFontCapabilities in fcfreetype.c.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V6.2.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover off-by-one errors in loops, bounds, and calculations before deployment.
Requiring documented development standards and tools can embed bounds-checking and arithmetic-correctness rules that stop off-by-one mistakes at introduction.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent off-by-one errors via reviews, static analysis, and testing.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect off-by-one errors before release.
Secure development life cycle includes requirements and reviews that can catch off-by-one errors.
Application security requirements can specify bounds-checking and input validation to prevent off-by-one errors.
Secure system architecture and engineering principles promote defensive coding practices that reduce off-by-one mistakes.
Secure coding directly addresses off-by-one errors through coding standards and peer review.