CVE-2026-77866SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts
Updated under an hour ago ()
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It affects Slab safeurl. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 9.0 CRITICAL (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N
- Weakness (CWE)
- CWE-918, CWE-636
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- EEF
- NVD analysis
- Awaiting Analysis
- Record last updated
- Sep 21, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Slab safeurl slab:safeurl | from 0.1.0 | CNA record |
References
- https://cna.erlef.org/cves/CVE-2026-77866.htmlrelated, third-party-advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-77866related
- https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70related
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.