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Vulnerability record · CVE-2025-56005 · published 20 January 2026

CVE-2025-56005: Dabeaz ply deserialization of untrusted data vulnerability

DDabeaz · Ply

An undocumented and unsafe feature in the PLY (Python Lex-Yacc) library 3.11 allows Remote Code Execution (RCE) via the `picklefile` parameter in the `yacc()` function. This parameter accepts a `.pkl` file that is deserialized with `pickle.load()` without validation. Because `pickle` allows execution of embedded code via `__reduce__()`, an attacker can achieve code execution by passing a malicious pickle file. The parameter is not mentioned in official documentation or the GitHub repository, yet it is active in the PyPI version. This introduces a stealthy backdoor and persistence risk. NOTE: A third-party states that this vulnerability should be rejected because the proof of concept does not demonstrate arbitrary code execution and fails to complete successfully.

9.8 CVSS 3.1 Critical EPSS 19% · top 2.8% CWE-502 · Deserialization of untrusted data
9.8CVSS 3.1 base score
19%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
13References, 6 tagged exploit
17 Sep 2026Last modified by NVD

Description

An undocumented and unsafe feature in the PLY (Python Lex-Yacc) library 3.11 allows Remote Code Execution (RCE) via the `picklefile` parameter in the `yacc()` function. This parameter accepts a `.pkl` file that is deserialized with `pickle.load()` without validation. Because `pickle` allows execution of embedded code via `__reduce__()`, an attacker can achieve code execution by passing a malicious pickle file. The parameter is not mentioned in official documentation or the GitHub repository, yet it is active in the PyPI version. This introduces a stealthy backdoor and persistence risk. NOTE: A third-party states that this vulnerability should be rejected because the proof of concept does not demonstrate arbitrary code execution and fails to complete successfully.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/bohmiiidd/Undocumented-RCE-in-PLY ExploitThird Party Advisory
https://github.com/bohmiiidd/Undocumument_RCE_PLY-yacc-CVE-2025-56005 ExploitThird Party Advisory
https://github.com/tom025/ply_exploit_rejection ExploitMitigationThird Party Advisory
https://github.com/tom025/ply_exploit_rejection/issues/1
http://www.openwall.com/lists/oss-security/2026/01/23/4 ExploitMailing List
http://www.openwall.com/lists/oss-security/2026/01/23/5 Mailing List
http://www.openwall.com/lists/oss-security/2026/01/28/5 ExploitMailing List
http://www.openwall.com/lists/oss-security/2026/01/29/1 ExploitMailing List
http://www.openwall.com/lists/oss-security/2026/01/29/2 Mailing List
http://www.openwall.com/lists/oss-security/2026/01/30/1
https://access.redhat.com/security/cve/CVE-2025-56005
https://bugzilla.redhat.com/show_bug.cgi?id=2431308
https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-56005.json

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Source: NIST National Vulnerability Database (record CVE-2025-56005), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.