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 CPE status
Linux-PAM Linux-PAM Affected: 0 , ≤ 1.7.2 (semver)
guessed 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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      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-54411\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-06-15T16:59:25.401303Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-06-15T16:59:29.063Z\"}}], \"cna\": {\"title\": \"Linux-PAM pam_userdb Observable Timing Discrepancy in Plaintext Password Comparison\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Xurshidbek Sobirjonov\"}], \"impacts\": [{\"descriptions\": [{\"lang\": \"en\", \"value\": \"An attacker who can repeatedly drive authentication through a service that invokes pam_userdb with plaintext-password configuration and without an artificial failure delay can measure response-timing differences to learn the correct password length and recover the plaintext password byte by byte. Recovery requires many measurements per character and is sensitive to scheduling and network jitter; recovery of one user\u0027s secret does not by itself yield access to other accounts. Practical exploitation is gated by an administrative misconfiguration (pam_userdb storing passwords in plaintext, reached when the module is configured with crypt=none, with an unknown crypt method, or with no crypt= option) and by the absence of failure-delay or rate-limiting in the calling service.\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"Safety\": \"NOT_DEFINED\", \"version\": \"4.0\", \"Recovery\": \"NOT_DEFINED\", \"baseScore\": 6.9, \"Automatable\": \"NO\", \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"valueDensity\": \"DIFFUSE\", \"vectorString\": \"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\", \"exploitMaturity\": \"PROOF_OF_CONCEPT\", \"providerUrgency\": \"NOT_DEFINED\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"attackRequirements\": \"PRESENT\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"HIGH\", \"vulnerabilityResponseEffort\": \"NOT_DEFINED\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"An attacker repeatedly authenticates through a service that calls pam_userdb (plaintext mode) and measures the time the service takes to reject each candidate password to learn the password length and recover the password one byte at a time.\"}]}, {\"format\": \"CVSS\", \"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 5.9, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N\", \"integrityImpact\": \"NONE\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"availabilityImpact\": \"NONE\", \"privilegesRequired\": \"NONE\", \"confidentialityImpact\": \"HIGH\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"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\"}], \"x_author\": \"Xurshidbek Sobirjonov\", \"datePublic\": \"2026-06-14T17:21:43.853Z\", \"references\": [{\"url\": \"https://github.com/linux-pam/linux-pam\", \"name\": \"Linux-PAM - upstream repository\", \"tags\": [\"product\"]}, {\"url\": \"https://github.com/linux-pam/linux-pam/blob/master/modules/pam_userdb/pam_userdb.c#L327\", \"name\": \"Vulnerable plaintext-password comparison in pam_userdb.c (master)\", \"tags\": [\"product\"]}, {\"url\": \"https://github.com/linux-pam/linux-pam/blob/master/libpam/include/pam_inline.h\", \"name\": \"pam_consttime_streq helper available for the remediation\", \"tags\": [\"product\"]}, {\"url\": \"https://cwe.mitre.org/data/definitions/208.html\", \"name\": \"CWE-208: Observable Timing Discrepancy\", \"tags\": [\"technical-description\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"Linux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pam_userdb module\u0027s 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.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eLinux-PAM through 1.7.2 contains an observable timing discrepancy (CWE-208) in the pam_userdb module\u0027s 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.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-208\", \"description\": \"CWE-208 Observable Timing Discrepancy\"}]}], \"providerMetadata\": {\"orgId\": \"309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c\", \"shortName\": \"TuranSec\", \"dateUpdated\": \"2026-08-10T11:43:56.355Z\"}, \"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.\"}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-54411\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-10T11:43:56.355Z\", \"dateReserved\": \"2026-06-13T16:39:46.122Z\", \"assignerOrgId\": \"309f9ea4-e3e9-4c6c-b79d-e8eb01244f2c\", \"datePublished\": \"2026-06-14T17:21:43.853Z\", \"assignerShortName\": \"TuranSec\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Taxonomy of the tags.





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

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.