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TI-2026-26073 Aliases CVE-2026-33693GHSA-q537-8fr5-cw35

Lemmy's Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid()

Priority HIGH 68CWE-918Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.

Summary

Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.7.0-beta.9, the `v4_is_invalid()` function in `activitypub-federation-rust` (`src/utils.rs`) does not check for `Ipv4Addr::UNSPECIFIED` (0.0.0.0). An unauthenticated attacker controlling a remote domain can point it to 0.0.0.0, bypass the SSRF protection introduced by the fix for CVE-2025-25194 (GHSA-7723-35v7-qcxw), and reach localhost services on the target server. Version 0.7.0-beta.9 patches the issue.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00373 31st percentileScored 2026-11-07
Fix Fixed lemmy (LemmyNet): 0.7.0-beta.9activitypub_federation (crates.io): 0.7.0-beta.9

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
LemmyNetlemmybefore 0.7.0-beta.90.7.0-beta.9Patch availableCNA
—activitypub_federation (crates.io)before 0.7.0-beta.90.7.0-beta.9Patch availableGHSA-q537-8fr5-cw35
  • lemmy VendorLemmyNet Affected before 0.7.0-beta.9 Fixed in 0.7.0-beta.9 Patch available CNA
  • activitypub_federation (crates.io) Vendor— Affected before 0.7.0-beta.9 Fixed in 0.7.0-beta.9 Patch available GHSA-q537-8fr5-cw35

Remediation

  • Fix · CNA lemmy (LemmyNet) Fixed in 0.7.0-beta.9
  • Fix · GHSA-q537-8fr5-cw35 activitypub_federation (crates.io) Fixed in 0.7.0-beta.9 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-33693
  2. 2026-10-03 Alias added: GHSA-q537-8fr5-cw35

References

Advisory 2

Other 3

  • TI-2026-23295 Lemmy: Unauthenticated SSRF via file_type query parameter injection in image endpoint CVSS 4.0HIGH 7.7
  • TI-2026-39555 Lemmy: Stored XSS via markdown image alt-text in lemmy-ui html5-embed CVSS 4.0MEDIUM 6.4
  • TI-2026-39552 Lemmy: Lower-ranked federated moderator can remove higher-ranked moderators CVSS 3.1MEDIUM 6.5
  • TI-2026-30504 Lemmy: SSRF and internal image disclosure in post link metadata via unvalidated og:image CVSS 3.1MEDIUM 6.5
  • TI-2026-39553 Lemmy: Blocked users can edit private messages sent before the block CVSS 4.0MEDIUM 5.3
  • TI-2026-39554 Lemmy: `CollectionAdd::Featured` does not check the post is in the community CVSS 4.0MEDIUM 5.1
See all 10 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences