CVE-2026-77866 SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts
Attackers can bypass SSRF protections in the safeurl library by using IPv6 addresses or unresolvable hosts to reach blocked internal network destinations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-77866?
CVE-2026-77866 is a critical server-side request forgery vulnerability in Slab safeurl, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Server-Side Request Forgery (SSRF) vulnerability in Slab safeurl allows an attacker who controls a validated URL to reach internal network destinations the library is configured to block.
Only IPv4 addresses are matched against the reserved ranges and the blocklist. Every other address is treated as matching nothing, so a destination that is rejected in its IPv4 form is accepted when written as an IPv6 address, IPv6 entries in the blocklist never match, and a host that resolves to no IPv4 address is accepted regardless of where it points. Deployments that rely on the allowlist instead are unaffected, because there an unmatched address is rejected.
This issue affects safeurl: from 0.1.0 onward.
Which versions are affected by CVE-2026-77866?
1 open source package ship an affected version, including safeurl.
| Package | Affected | Fixed in |
|---|---|---|
safeurl Hex | From 0.1.0 | None |
How do I fix CVE-2026-77866?
No fix has been published for CVE-2026-77866 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-77866 being exploited?
There is no known exploitation of CVE-2026-77866 in the wild and no public exploit code.
Sources
Also known as EEF-CVE-2026-77866, GHSA-97fv-h8pq-9grg.