CVE-2026-54411 (GCVE-0-2026-54411)

Vulnerability from cvelistv5 – Published: 2026-06-14 17:21 – Updated: 2026-08-10 11:43
VLAI
Title
Linux-PAM pam_userdb Observable Timing Discrepancy in Plaintext Password Comparison
Summary
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.
Severity
6.9 (Medium)
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P/AU:N/V:D
5.9 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-06-15 16:59 UTC
CWE
  • CWE-208 - Observable Timing Discrepancy
Assigner
References
Impacted products
Vendor Product Version
Linux-PAM Linux-PAM Affected: 0 , ≤ 1.7.2 (semver)
Create a notification for this product.
Date Public
2026-06-14 17:21
Credits
Xurshidbek Sobirjonov
Show details on NVD website
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                {
                  "lang": "en",
                  "value": "GENERAL"
                }
              ]
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-208",
                  "description": "CWE-208 Observable Timing Discrepancy",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-10T11:43:56.355Z",
            "orgId": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
            "shortName": "TuranSec"
          },
          "references": [
            {
              "name": "Linux-PAM - upstream repository",
              "tags": [
                "product"
              ],
              "url": "https://github.com/linux-pam/linux-pam"
            },
            {
              "name": "Vulnerable plaintext-password comparison in pam_userdb.c (master)",
              "tags": [
                "product"
              ],
              "url": "https://github.com/linux-pam/linux-pam/blob/master/modules/pam_userdb/pam_userdb.c#L327"
            },
            {
              "name": "pam_consttime_streq helper available for the remediation",
              "tags": [
                "product"
              ],
              "url": "https://github.com/linux-pam/linux-pam/blob/master/libpam/include/pam_inline.h"
            },
            {
              "name": "CWE-208: Observable Timing Discrepancy",
              "tags": [
                "technical-description"
              ],
              "url": "https://cwe.mitre.org/data/definitions/208.html"
            }
          ],
          "source": {
            "discovery": "EXTERNAL"
          },
          "title": "Linux-PAM pam_userdb Observable Timing Discrepancy in Plaintext Password Comparison",
          "x_assigner_notes": "The vulnerable comparison was verified by direct source inspection of modules/pam_userdb/pam_userdb.c at tag v1.7.2 and at master HEAD as of disclosure: lines 327-332 perform a length-equality early exit followed by strncmp() / strncasecmp(). Linux-PAM has previously addressed the same weakness class in a sibling module: NEWS for Release 1.7.0 records \"pam_unix: compare password hashes in constant time\", and Release 1.6.0 hardened pam_mkhomedir \"against timing attacks\". The pam_consttime_streq() helper used by those fixes lives in libpam/include/pam_inline.h, which pam_userdb.c already includes, so the remediation in pam_userdb is a drop-in replacement of the strncmp call. The v1.7.2 release notes do not list a pam_userdb hardening change. Exploitation is gated by (a) the administrator having configured pam_userdb with plaintext password storage (crypt=none, unknown crypt method, or no crypt= option), a discouraged but documented configuration; and (b) the calling service not applying an authentication-failure delay - both gates raise attack complexity and bound real-world impact, so CVSS is scored MEDIUM rather than HIGH consistent with prior CWE-208 timing-leak CVE scoring.",
          "x_author": "Xurshidbek Sobirjonov"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c",
        "assignerShortName": "TuranSec",
        "cveId": "CVE-2026-54411",
        "datePublished": "2026-06-14T17:21:43.853Z",
        "dateReserved": "2026-06-13T16:39:46.122Z",
        "dateUpdated": "2026-08-10T11:43:56.355Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.