CVE-2026-34085
Description
A flaw was found in fontconfig. This vulnerability, an off-by-one error in how fontconfig handles font capabilities, could allow a local attacker to cause a one-byte out-of-bounds write. This issue may lead to a system crash, resulting in a Denial of Service (DoS), or potentially enable the attacker to execute unauthorized code.
Statement
This vulnerability is rated Moderate severity by Red Hat Product Security. The issue arises from a memory handling flaw in font processing, which can cause applications such as fc-cache to crash when processing a specially crafted font file.
Exploitation requires a user to install or process a malicious font, meaning the issue cannot be triggered remotely without user interaction. While the crash may disrupt system functionality: for example, affecting graphical login services or applications that rely on font rendering, the impact is limited to application stability.
The underlying flaw involves a very small memory overwrite (one byte), which significantly limits the ability to exploit it for more serious outcomes such as executing arbitrary code or fully compromising the system. There is no evidence that the vulnerability can be reliably used to gain control over a system or access sensitive data.
Red Hat therefore assesses the primary impact as a denial of service in user-space components, resulting in a Moderate severity rating.
Mitigation
Red Hat is not aware of a practical temporary workaround that fully mitigates this issue or meets Red Hat Product Security's standards for usability, deployment, applicability, or stability.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.6 | 7.8 | 5.9 |
| Attack Vector | Local | Local | Local |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | Low | None |
| User Interaction | Required | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | Low | High | Low |
| Integrity Impact | Low | High | Low |
| Availability Impact | High | High | Low |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Instability
This weakness will generally lead to undefined behavior and therefore crashes. In the case of overflows involving loop index variables, the likelihood of infinite loops is also high.
Integrity
Technical Impact: Modify Memory
If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the wrap around results in other conditions such as buffer overflows, further memory corruption may occur.
Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism
This weakness can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.
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