FKIE_CVE-2026-54740

Vulnerability from fkie_nvd - Published: 2026-08-19 21:16 - Updated: 2026-08-20 20:17
Severity
6.5 (Medium) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Summary
Lemmy is a link aggregator and forum for the fediverse. Prior to 0.19.19 and 1.0.0-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18.
References
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/pull/6475
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/pull/6478
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-alpha.18
security-advisories@github.comhttps://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7
security-advisories@github.comhttps://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19
134c704f-9b21-4f2e-91b3-4a467353bcc0https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7
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-alpha.18"
            }
          ]
        }
      ],
      "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-alpha.18, a lower-ranked remote moderator can remove a higher-ranked moderator by sending a signed ActivityPub Remove activity to the target instance. The local API uses LocalUser::is_higher_mod_or_admin_check to enforce moderator rank, but CollectionRemove::verify in crates/apub/activities/src/community/collection_remove.rs only calls verify_mod_action. CollectionRemove::receive dereferences self.object as an ApubPerson, creates a CommunityModeratorForm, and calls CommunityActions::leave without checking that the actor outranks the moderator identified by the object field. In communities with federated moderators, a junior moderator can therefore strip senior moderators from the community moderator list even though the local API rejects the same action. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.18."
    }
  ],
  "id": "CVE-2026-54740",
  "lastModified": "2026-08-20T20:17:35.273",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-54740",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-20T19:57:07.165095Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-19T21:16:58.363",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/commit/d127e714a66f34f6b9c8ea15f20097ac907cdf28"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/commit/ede1d348344ca2027fd1bc6a0cab25575c0c3a4c"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/pull/6475"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/pull/6478"
    },
    {
      "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-alpha.18"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-xmpx-2j2f-c7g7"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-862"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}



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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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