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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-33693: 0.37% estimated exploitation activity in the next 30 days; percentile 31.32 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The v4isinvalid() 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. Details File: src/utils.rs in activitypub-federation-rust Function: v4isinvalid(v4: Ipv4Addr) - bool The function checks isprivate(), isloopback(), islinklocal(), ismulticast(), and isdocumentation() — but omits isunspecified(). On Linux, macOS, and Windows, TCP connections to 0.0.0.0 are routed to localhost (127.0.0.1). Additionally, ::ffff:0.0.0.0 (IPv4-mapped IPv6) also bypasses because v6isinvalid() calls toipv4mapped().issomeand(v4isinvalid), inheriting the same gap. Notably, v6isinvalid() already includes isunspecified() for native IPv6, making this an asymmetric oversight. Independent secondary finding — DNS Rebinding TOCTOU:…

Published by the source

25 Mar 2026, 20:23 UTC

Last modified by the source

27 Mar 2026, 21:36 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-q537-8fr5-cw35

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# Patch Next advisory brief: CVE-2026-33693

Advisory: Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid()
IDs: CVE-2026-33693, GHSA-q537-8fr5-cw35
Record: https://patchnext.com/advisories/cve-2026-33693 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: activitypub_federation 0.7.0-beta.9. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io activitypub_federation: affected < 0.7.0-beta.9; fixed in 0.7.0-beta.9

## Suggested inspection (read-only)
- crates.io activitypub_federation: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on activitypub_federation.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-q537-8fr5-cw35 (GitHub-reviewed advisory GHSA-q537-8fr5-cw35 lists affected ranges: crates.io activitypub_federation >=0 <0.7.0-beta.9)

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