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CVE-2026-56390— Arbitrary Output Location Change in GNU Bison

Quick assessment

Affected
GNU Bison
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

GNU bison是美国GNU基金会开源的一种通用语法分析器生成工具。 GNU Bison 3.8.2版本存在输入验证错误漏洞，该漏洞源于对语法定义的输出路径处理不当，%output和%header等语法指令允许指定文件路径且未加限制，导致生成的文件可以被写入任意可写位置，可能覆盖现有文件。

CVSS 4.6 · Medium EPSS 0.18% · P7

Affected Version Matrix 1

VendorProduct Version RangeStatus
GNU Bison 3.8.2 affected
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I. Basic Information for CVE-2026-56390

Vulnerability Information
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Vulnerability Title
Arbitrary Output Location Change in GNU Bison
Source: CVE Program / CVE List V5
Vulnerability Description
GNU Bison improperly handles grammar‑defined output paths. Grammar directives such as %output and %header allow specifying file paths, which are accepted without restriction and override caller‑supplied output options. When processing attacker-supplied grammar, this behavior allows directing generated files to arbitrary writable locations on the filesystem, potentially overwriting existing files accessible to the Bison process. Maintainers of this project were notified about this vulnerability, and fixed the issue in commit 8d101c19d4d9aaedf83a448c925513742d4efcf0. However, they did not provide vulnerable version range. Version 3.8.2 was tested and confirmed as vulnerable, other versions were not tested but might also be vulnerable.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
文件名或路径的外部可控制
Source: CVE Program / CVE List V5
Vulnerability Title
GNU Bison 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
GNU bison是美国GNU基金会开源的一种通用语法分析器生成工具。 GNU Bison 3.8.2版本存在输入验证错误漏洞，该漏洞源于对语法定义的输出路径处理不当，%output和%header等语法指令允许指定文件路径且未加限制，导致生成的文件可以被写入任意可写位置，可能覆盖现有文件。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
GNU Bison 3.8.2 -

II. Public POCs for CVE-2026-56390

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III. Intelligence Information for CVE-2026-56390

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Patches & Fixes for CVE-2026-56390 (1)

Security Blog Posts for CVE-2026-56390 (1)

IV. Related Vulnerabilities

Same product: Bison
Same vendor: GNU
Same weakness: CWE-73

V. Comments for CVE-2026-56390

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