FKIE_CVE-2026-54739

Vulnerability from fkie_nvd - Published: 2026-08-19 21:16 - Updated: 2026-08-21 22:16
Severity
6.9 (Medium) - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
Summary
Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, Lemmy's login endpoint in crates/api/api/src/local_user/login.rs returns different errors depending on whether the username_or_email value exists. LocalUserView::find_by_email_or_name propagates a NotFound response for an unknown account, while an existing account with a wrong password returns LemmyErrorType::IncorrectLogin. This observable response discrepancy, including HTTP 404 for a nonexistent account and HTTP 400 for an incorrect password on an existing account, allows an unauthenticated attacker to confirm registered usernames or email addresses and use the results for targeted credential attacks or social engineering. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1.
References
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/commit/4d235a1b668b7dda6b73dbbc9ca289bb40acfa83
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/commit/59e968a5ac36d36d08a59028e2dbb92641536964
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/pull/6531
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/pull/6535
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/releases/tag/0.19.19
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/releases/tag/1.0.0-beta.1
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/security/advisories/GHSA-xgg7-8hvq-8m65
security-advisories@github.comhttps://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "lemmy",
          "vendor": "LemmyNet",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.19.19"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-alpha.0, \u003c 1.0.0-beta.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-beta.1, Lemmy\u0027s login endpoint in crates/api/api/src/local_user/login.rs returns different errors depending on whether the username_or_email value exists. LocalUserView::find_by_email_or_name propagates a NotFound response for an unknown account, while an existing account with a wrong password returns LemmyErrorType::IncorrectLogin. This observable response discrepancy, including HTTP 404 for a nonexistent account and HTTP 400 for an incorrect password on an existing account, allows an unauthenticated attacker to confirm registered usernames or email addresses and use the results for targeted credential attacks or social engineering. This issue is fixed in versions 0.19.19 and 1.0.0-beta.1."
    }
  ],
  "id": "CVE-2026-54739",
  "lastModified": "2026-08-21T22:16:40.773",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 6.9,
          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/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:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "LOW",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-54739",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-21T21:09:48.318270Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-19T21:16:58.227",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/commit/4d235a1b668b7dda6b73dbbc9ca289bb40acfa83"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/commit/59e968a5ac36d36d08a59028e2dbb92641536964"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/pull/6531"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/pull/6535"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/releases/tag/0.19.19"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-beta.1"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xgg7-8hvq-8m65"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-204"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}



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