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Back to active CVEs
High · CVSS 8.6CVE-2026-55103

Discourse ActivityPub: Fix inbound actor validation and apply outbound request SSRF hardeningCVE-2026-55103

Answer in brief

CVE-2026-55103 records a High severity (CVSS 8.6) vulnerability in Discourse ActivityPub: Fix inbound actor validation and apply outbound request SSRF hardening. The current sources do not mark it as known exploited. The current feed maps discourse/discourse-activity-pub (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 15, 2026Updated Oct 15, 2026Source checked Oct 15, 2026First seen by HOL Oct 15, 2026Material review Oct 15, 2026
Upstream Advisory

Key facts

Risk
High · CVSS 8.6
Exploitation
Not marked as known exploited
Affected software
1 mapped package or product
Fix availability
Available

Why this deserves its current priority

CVSS is 8.6. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps discourse/discourse-activity-pub (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
discourse/discourse-activity-pubgeneric<1c8518b0f2abdf31cbea3e0b242f74d8994a9ba51c8518b0f2abdf31cbea3e0b242f74d8994a9ba5

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for discourse/discourse-activity-pub.
  2. 2Review the reported fix. Update discourse/discourse-activity-pub to 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Oct 15, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Oct 15, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Oct 15, 2026

Sources and claim methodology

  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
Upstream source description

Discourse ActivityPub adds ActivityPub support to Discourse. Prior to commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5, inbound ActivityPub processing does not sufficiently verify that the actor authenticated by the signed request matches the Activity actor and owns the referenced federated post. A remote attacker can exploit these missing identity and ownership checks to edit, delete, or reply to federated posts without the required permissions. This vulnerability is fixed with commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5.

Quoted source text, attributed separately from HOL analysis.

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  • libp2p: Single pre-auth STUN packet terminates `@libp2p/webrtc` WebRTC-direct Node.js listenersSame generic ecosystem
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Record context

Vulnerability class
SSRF
EPSS
Not reported
CWE IDs
CWE-345, CWE-863
Source
CVE List V5
Source checked
Oct 15, 2026
References
2 linked sources
Open source record