CVE-2026-54742 (GCVE-0-2026-54742)
Vulnerability from cvelistv5 – Published: 2026-08-19 20:10 – Updated: 2026-08-20 20:01
VLAI
EPSS
VEX
Title
Lemmy: `CollectionAdd::Featured` does not check the post is in the community
Summary
Lemmy is a link aggregator and forum for the fediverse. From 0.19.18 until 0.19.19 and 1.0.0-alpha.20, a community moderator can feature or unfeature posts in other communities through federated CollectionAdd and CollectionRemove activities using CollectionType::Featured. After verify_mod_action authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collection_add.rs and crates/apub/activities/src/community/collection_remove.rs dereference self.object as an ApubPost and update featured_community without verifying that post.community_id equals community.id. A moderator can therefore target an unrelated post owned by another community, push it into featured feeds and listings, or undo another community's legitimate curation decision. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.20.
Severity
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-20 20:01 UTC
CWE
- CWE-863 - Incorrect Authorization
Assigner
References
8 references
| URL | Tags |
|---|---|
| https://github.com/LemmyNet/lemmy/security/adviso… | x_refsource_CONFIRM |
| https://github.com/LemmyNet/lemmy/pull/6500 | x_refsource_MISC |
| https://github.com/LemmyNet/lemmy/pull/6501 | x_refsource_MISC |
| https://github.com/LemmyNet/lemmy/commit/108d78c5… | x_refsource_MISC |
| https://github.com/LemmyNet/lemmy/commit/abe25624… | x_refsource_MISC |
| https://github.com/LemmyNet/lemmy/releases/tag/0.19.19 | x_refsource_MISC |
| https://github.com/LemmyNet/lemmy/releases/tag/1.… | x_refsource_MISC |
| https://join-lemmy.org/news/2026-06-09_-_Lemmy_Re… | x_refsource_MISC |
Impacted products
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-54742",
"options": [
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"Exploitation": "poc"
},
{
"Automatable": "no"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-08-20T20:01:14.417876Z",
"version": "2.0.3"
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"dateUpdated": "2026-08-20T20:01:19.950Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"references": [
{
"tags": [
"exploit"
],
"url": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v"
}
],
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"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.20"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "Lemmy is a link aggregator and forum for the fediverse. From 0.19.18 until 0.19.19 and 1.0.0-alpha.20, a community moderator can feature or unfeature posts in other communities through federated CollectionAdd and CollectionRemove activities using CollectionType::Featured. After verify_mod_action authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collection_add.rs and crates/apub/activities/src/community/collection_remove.rs dereference self.object as an ApubPost and update featured_community without verifying that post.community_id equals community.id. A moderator can therefore target an unrelated post owned by another community, push it into featured feeds and listings, or undo another community\u0027s legitimate curation decision. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.20."
}
],
"metrics": [
{
"cvssV4_0": {
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 5.1,
"baseSeverity": "MEDIUM",
"privilegesRequired": "HIGH",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N",
"version": "4.0",
"vulnAvailabilityImpact": "NONE",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "LOW"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-863",
"description": "CWE-863: Incorrect Authorization",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-19T20:10:56.632Z",
"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"shortName": "GitHub_M"
},
"references": [
{
"name": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v",
"tags": [
"x_refsource_CONFIRM"
],
"url": "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v"
},
{
"name": "https://github.com/LemmyNet/lemmy/pull/6500",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/LemmyNet/lemmy/pull/6500"
},
{
"name": "https://github.com/LemmyNet/lemmy/pull/6501",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/LemmyNet/lemmy/pull/6501"
},
{
"name": "https://github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23"
},
{
"name": "https://github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5"
},
{
"name": "https://github.com/LemmyNet/lemmy/releases/tag/0.19.19",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/LemmyNet/lemmy/releases/tag/0.19.19"
},
{
"name": "https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.20",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.20"
},
{
"name": "https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19",
"tags": [
"x_refsource_MISC"
],
"url": "https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19"
}
],
"source": {
"advisory": "GHSA-gwfj-h8r7-792v",
"discovery": "UNKNOWN"
},
"title": "Lemmy: `CollectionAdd::Featured` does not check the post is in the community"
}
},
"cveMetadata": {
"assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"assignerShortName": "GitHub_M",
"cveId": "CVE-2026-54742",
"datePublished": "2026-08-19T20:10:56.632Z",
"dateReserved": "2026-06-15T23:12:41.964Z",
"dateUpdated": "2026-08-20T20:01:19.950Z",
"state": "PUBLISHED"
},
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"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-54742",
"date": "2026-08-25",
"epss": "0.00419",
"percentile": "0.34713"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-54742\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-08-19T20:17:17.093\",\"lastModified\":\"2026-08-20T20:17:35.410\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"Lemmy is a link aggregator and forum for the fediverse. From 0.19.18 until 0.19.19 and 1.0.0-alpha.20, a community moderator can feature or unfeature posts in other communities through federated CollectionAdd and CollectionRemove activities using CollectionType::Featured. After verify_mod_action authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collection_add.rs and crates/apub/activities/src/community/collection_remove.rs dereference self.object as an ApubPost and update featured_community without verifying that post.community_id equals community.id. A moderator can therefore target an unrelated post owned by another community, push it into featured feeds and listings, or undo another community\u0027s legitimate curation decision. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.20.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"LemmyNet\",\"product\":\"lemmy\",\"versions\":[{\"version\":\"\u003c 0.19.19\",\"status\":\"affected\"},{\"version\":\"\u003e= 1.0.0-alpha.0, \u003c 1.0.0-alpha.20\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV40\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"4.0\",\"vectorString\":\"CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/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\",\"baseScore\":5.1,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"attackRequirements\":\"NONE\",\"privilegesRequired\":\"HIGH\",\"userInteraction\":\"NONE\",\"vulnConfidentialityImpact\":\"NONE\",\"vulnIntegrityImpact\":\"LOW\",\"vulnAvailabilityImpact\":\"NONE\",\"subConfidentialityImpact\":\"NONE\",\"subIntegrityImpact\":\"NONE\",\"subAvailabilityImpact\":\"NONE\",\"exploitMaturity\":\"NOT_DEFINED\",\"confidentialityRequirement\":\"NOT_DEFINED\",\"integrityRequirement\":\"NOT_DEFINED\",\"availabilityRequirement\":\"NOT_DEFINED\",\"modifiedAttackVector\":\"NOT_DEFINED\",\"modifiedAttackComplexity\":\"NOT_DEFINED\",\"modifiedAttackRequirements\":\"NOT_DEFINED\",\"modifiedPrivilegesRequired\":\"NOT_DEFINED\",\"modifiedUserInteraction\":\"NOT_DEFINED\",\"modifiedVulnConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedVulnIntegrityImpact\":\"NOT_DEFINED\",\"modifiedVulnAvailabilityImpact\":\"NOT_DEFINED\",\"modifiedSubConfidentialityImpact\":\"NOT_DEFINED\",\"modifiedSubIntegrityImpact\":\"NOT_DEFINED\",\"modifiedSubAvailabilityImpact\":\"NOT_DEFINED\",\"Safety\":\"NOT_DEFINED\",\"Automatable\":\"NOT_DEFINED\",\"Recovery\":\"NOT_DEFINED\",\"valueDensity\":\"NOT_DEFINED\",\"vulnerabilityResponseEffort\":\"NOT_DEFINED\",\"providerUrgency\":\"NOT_DEFINED\"}}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-08-20T20:01:14.417876Z\",\"id\":\"CVE-2026-54742\",\"options\":[{\"exploitation\":\"poc\"},{\"automatable\":\"no\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-863\"}]}],\"references\":[{\"url\":\"https://github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/LemmyNet/lemmy/pull/6500\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/LemmyNet/lemmy/pull/6501\",\"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.20\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v\",\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\"}]}}",
"vulnrichment": {
"containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-54742\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-20T20:01:14.417876Z\"}}}], \"references\": [{\"url\": \"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v\", \"tags\": [\"exploit\"]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-20T20:00:59.326Z\"}}], \"cna\": {\"title\": \"Lemmy: `CollectionAdd::Featured` does not check the post is in the community\", \"source\": {\"advisory\": \"GHSA-gwfj-h8r7-792v\", \"discovery\": \"UNKNOWN\"}, \"metrics\": [{\"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 5.1, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"NONE\", \"privilegesRequired\": \"HIGH\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"LOW\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"NONE\"}}], \"affected\": [{\"vendor\": \"LemmyNet\", \"product\": \"lemmy\", \"versions\": [{\"status\": \"affected\", \"version\": \"\u003c 0.19.19\"}, {\"status\": \"affected\", \"version\": \"\u003e= 1.0.0-alpha.0, \u003c 1.0.0-alpha.20\"}]}], \"references\": [{\"url\": \"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v\", \"name\": \"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-gwfj-h8r7-792v\", \"tags\": [\"x_refsource_CONFIRM\"]}, {\"url\": \"https://github.com/LemmyNet/lemmy/pull/6500\", \"name\": \"https://github.com/LemmyNet/lemmy/pull/6500\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/LemmyNet/lemmy/pull/6501\", \"name\": \"https://github.com/LemmyNet/lemmy/pull/6501\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23\", \"name\": \"https://github.com/LemmyNet/lemmy/commit/108d78c592cc88bac2b0bf52ca6631be54f6fb23\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5\", \"name\": \"https://github.com/LemmyNet/lemmy/commit/abe256243822526dcd4bca857f7c0adeb49944f5\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/LemmyNet/lemmy/releases/tag/0.19.19\", \"name\": \"https://github.com/LemmyNet/lemmy/releases/tag/0.19.19\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.20\", \"name\": \"https://github.com/LemmyNet/lemmy/releases/tag/1.0.0-alpha.20\", \"tags\": [\"x_refsource_MISC\"]}, {\"url\": \"https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19\", \"name\": \"https://join-lemmy.org/news/2026-06-09_-_Lemmy_Release_v0.19.19\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en\", \"value\": \"Lemmy is a link aggregator and forum for the fediverse. From 0.19.18 until 0.19.19 and 1.0.0-alpha.20, a community moderator can feature or unfeature posts in other communities through federated CollectionAdd and CollectionRemove activities using CollectionType::Featured. After verify_mod_action authorizes the actor against self.community(), the receive handlers in crates/apub/activities/src/community/collection_add.rs and crates/apub/activities/src/community/collection_remove.rs dereference self.object as an ApubPost and update featured_community without verifying that post.community_id equals community.id. A moderator can therefore target an unrelated post owned by another community, push it into featured feeds and listings, or undo another community\u0027s legitimate curation decision. This issue is fixed in versions 0.19.19 and 1.0.0-alpha.20.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-863\", \"description\": \"CWE-863: Incorrect Authorization\"}]}], \"providerMetadata\": {\"orgId\": \"a0819718-46f1-4df5-94e2-005712e83aaa\", \"shortName\": \"GitHub_M\", \"dateUpdated\": \"2026-08-19T20:10:56.632Z\"}}}",
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"dataType": "CVE_RECORD",
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}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
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.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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