6.9
MEDIUM
CVSS 4.0
CVE-2026-54411
Linux-PAM pam_userdb Observable Timing Discrepancy in Plaintext Password Comparison
Overview
Description
Linux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pam_userdb module's plaintext-password comparison path in modules/pam_userdb/pam_userdb.c that allows a local or network-adjacent attacker able to repeatedly drive authentication through a calling service to recover the plaintext password of a target account by measuring response-timing differences.
Details
INFO
Published Date :
June 14, 2026, 6:17 p.m.
Last Modified :
Aug. 10, 2026, 12:17 p.m.
Remotely Exploit :
Yes !
Source :
309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework
for assessing the severity of vulnerabilities in software and systems.
We collect and displays CVSS scores from various sources for each CVE.
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 4.0 | MEDIUM | 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c | ||||
| CVSS 4.0 | MEDIUM | 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c |
Solution
Configure pam_userdb to use a strong cryptographic method for password storage and comparison.
- Configure pam_userdb with a strong crypt method.
- Avoid using crypt=none or unrecognized methods.
- Ensure correct configuration of pam_userdb.
- Update the module if possible.
References
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-54411.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-54411 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-54411
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-54411 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-54411 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c
Aug. 10, 2026
Action Type Old Value New Value Changed Description Linux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pam_userdb module's plaintext-password comparison path in modules/pam_userdb/pam_userdb.c that allows a local or network-adjacent attacker able to repeatedly drive authentication through a calling service to recover the plaintext password of a target account by measuring response-timing differences. The comparison uses strncmp() (or strncasecmp() when PAM_ICASE_ARG is set) preceded by a length-equality check, so the time to reject a candidate depends on the index of the first differing byte and on whether the candidate's length matches the stored password, leaking the password length and individual prefix bytes. The vulnerable path is reached when the administrator configures pam_userdb with crypt=none, with an unrecognized crypt method, or without a crypt= argument, causing the module to store and compare credentials in plaintext. Linux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pam_userdb module's plaintext-password comparison path in modules/pam_userdb/pam_userdb.c that allows a local or network-adjacent attacker able to repeatedly drive authentication through a calling service to recover the plaintext password of a target account by measuring response-timing differences. -
CVE Translated by [email protected]
Jul. 24, 2026
Action Type Old Value New Value Changed Translation Title: Linux-PAM, Description: Linux-PAM hasta 1.7.2 contiene una discrepancia de tiempo observable (CWE-208) en la ruta de comparación de contraseñas en texto plano del módulo pam_userdb en modules/pam_userdb/pam_userdb.c que permite a un atacante local o adyacente a la red, capaz de impulsar repetidamente la autenticación a través de un servicio llamante, recuperar la contraseña en texto plano de una cuenta objetivo midiendo las diferencias de tiempo de respuesta. La comparación utiliza strncmp() (o strncasecmp() cuando PAM_ICASE_ARG está configurado) precedida por una verificación de igualdad de longitud, por lo que el tiempo para rechazar un candidato depende del índice del primer byte diferente y de si la longitud del candidato coincide con la contraseña almacenada, filtrando la longitud de la contraseña y los bytes de prefijo individuales. La ruta vulnerable se alcanza cuando el administrador configura pam_userdb con crypt=none, con un método crypt no reconocido, o sin un argumento crypt=, lo que hace que el módulo almacene y compare credenciales en texto plano. Title: Linux-PAM, Description: Linux-PAM hasta 1.7.2 contiene una discrepancia de tiempo observable (CWE-208) en la ruta de comparación de contraseñas en texto plano del módulo pam_userdb en modules/pam_userdb/pam_userdb.c que permite a un atacante local o adyacente a la red, capaz de impulsar repetidamente la autenticación a través de un servicio llamante, recuperar la contraseña en texto plano de una cuenta objetivo midiendo las diferencias de tiempo de respuesta. La comparación utiliza strncmp() (o strncasecmp() cuando PAM_ICASE_ARG está configurado) precedida por una verificación de igualdad de longitud, por lo que el tiempo para rechazar un candidato depende del índice del primer byte diferente y de si la longitud del candidato coincide con la contraseña almacenada, filtrando la longitud de la contraseña y los bytes de prefijo individuales. La ruta vulnerable se alcanza cuando el administrador configura pam_userdb con crypt=none, con un método crypt no reconocido, o sin un argumento crypt=, lo que hace que el módulo almacene y compare credenciales en texto plano. -
CVE Translated by [email protected]
Jul. 23, 2026
Action Type Old Value New Value Added Translation Title: Linux-PAM, Description: Linux-PAM hasta 1.7.2 contiene una discrepancia de tiempo observable (CWE-208) en la ruta de comparación de contraseñas en texto plano del módulo pam_userdb en modules/pam_userdb/pam_userdb.c que permite a un atacante local o adyacente a la red, capaz de impulsar repetidamente la autenticación a través de un servicio llamante, recuperar la contraseña en texto plano de una cuenta objetivo midiendo las diferencias de tiempo de respuesta. La comparación utiliza strncmp() (o strncasecmp() cuando PAM_ICASE_ARG está configurado) precedida por una verificación de igualdad de longitud, por lo que el tiempo para rechazar un candidato depende del índice del primer byte diferente y de si la longitud del candidato coincide con la contraseña almacenada, filtrando la longitud de la contraseña y los bytes de prefijo individuales. La ruta vulnerable se alcanza cuando el administrador configura pam_userdb con crypt=none, con un método crypt no reconocido, o sin un argumento crypt=, lo que hace que el módulo almacene y compare credenciales en texto plano. -
CVE Modified by 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://github.com/linux-pam/linux-pam', 'vendor': 'Linux-PAM', 'modules': ['pam_userdb'], 'product': 'Linux-PAM', 'versions': [{'status': 'affected', 'version': '0', 'versionType': 'semver', 'lessThanOrEqual': '1.7.2'}], 'programFiles': ['modules/pam_userdb/pam_userdb.c'], 'collectionURL': 'https://github.com/linux-pam/linux-pam', 'defaultStatus': 'unknown'}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-54411', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-15T16:59:25.401303Z'} -
New CVE Received by 309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c
Jun. 14, 2026
Action Type Old Value New Value Added Description Linux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pam_userdb module's plaintext-password comparison path in modules/pam_userdb/pam_userdb.c that allows a local or network-adjacent attacker able to repeatedly drive authentication through a calling service to recover the plaintext password of a target account by measuring response-timing differences. The comparison uses strncmp() (or strncasecmp() when PAM_ICASE_ARG is set) preceded by a length-equality check, so the time to reject a candidate depends on the index of the first differing byte and on whether the candidate's length matches the stored password, leaking the password length and individual prefix bytes. The vulnerable path is reached when the administrator configures pam_userdb with crypt=none, with an unrecognized crypt method, or without a crypt= argument, causing the module to store and compare credentials in plaintext. Added CVSS V4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:N/R:X/V:D/RE:X/U:X Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N Added CWE CWE-208 Added Reference https://cwe.mitre.org/data/definitions/208.html Added Reference https://github.com/linux-pam/linux-pam Added Reference https://github.com/linux-pam/linux-pam/blob/master/libpam/include/pam_inline.h Added Reference https://github.com/linux-pam/linux-pam/blob/master/modules/pam_userdb/pam_userdb.c#L327
EPSS is a daily estimate of the probability of exploitation activity
being observed over the next 30 days. Following chart shows the EPSS
score history of the vulnerability.