CVE-2026-33693 json
Lemmy's Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid()
published 2026-03-25 7 mo ago modified 2026-06-17 4 mo ago also GHSA-q537-8fr5-cw35 , EUVD-2026-16494
- cvss
- 6.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.4%
- EPSS 0.4% chance of exploitation in 30 days, percentile 31%
- public exploits
- 0
- none known
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.
Patch / fix
- crates.io activitypub_federation 0.7.0-beta.9
CISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 7 mo ago
Exploit prediction
0.37% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N |
| GitHub | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| crates.io | activitypub_federation | <0.7.0-beta.9 |
0.7.0-beta.9 |
Affected products
- LemmyNet lemmy
Classification
- Weakness
-
- CWE-918 Server-Side Request Forgery
References
-
github.com
/LemmyNet/activitypub-federation-rust/commit/4ae8532b17bc35755240b7f55d4a5b7665351599
web
-
github.com
/LemmyNet/lemmy/security/advisories/GHSA-q537-8fr5-cw35
web
-
github.com
/advisories/GHSA-7723-35v7-qcxw
advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-33693
advisory
-
github.com
/LemmyNet/activitypub-federation-rust
package
Sources
- CVE List CVE-2026-33693
- GitHub Advisory GHSA-q537-8fr5-cw35
- NVD CVE-2026-33693
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.