CVE-2026-56389
Description
A flaw was found in GNU Bison. During HTML report generation, the software improperly handles grammar-defined configuration variables. An attacker can provide a specially crafted grammar file that overrides the executable used for XML-to-HTML transformation. This allows for the execution of an arbitrary program with the privileges of the Bison process, leading to arbitrary code execution.
Statement
This is a Moderate arbitrary code execution flaw in GNU Bison. The vulnerability arises when the bison --html command processes a specially crafted grammar file, enabling an attacker to define and execute an arbitrary program with the privileges of the Bison process. Exploitation requires user interaction to process a malicious grammar file, which limits the attack surface to scenarios where untrusted input is explicitly processed.
Mitigation
To mitigate this vulnerability, avoid processing untrusted or unverified grammar files with the `bison --html` command. Restrict the use of `bison --html` to trusted input sources only. This operational control reduces the risk of arbitrary code execution by preventing the vulnerable code path from being triggered with malicious input.
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.5 | 8.6 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Unchanged | Changed | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | None | High | N/A |
| Availability Impact | None | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
NVD: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality,Integrity,Availability,Non-Repudiation
Technical Impact: Execute Unauthorized Code or Commands; DoS: Crash, Exit, or Restart; Read Files or Directories; Modify Files or Directories; Read Application Data; Modify Application Data; Hide Activities
Attackers could execute unauthorized operating system commands, which could then be used to disable the product, or read and modify data for which the attacker does not have permissions to access directly. Since the targeted application is directly executing the commands instead of the attacker, any malicious activities may appear to come from the application or the application's owner.
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