Raw vector
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-77866 is a critical-severity Failing Open (CWE-636) vulnerability in Erlef (inferred from references). Its CVSS base score is 9.0 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 39th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and CP-12 (Safe Mode) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-78678
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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Mitigating Controls (NIST 800-53 r5) AI
Information flow enforcement can restrict which destinations the server is allowed to contact on behalf of users.
CP-12 forces entry into a safe mode on detected conditions, limiting exposure but not covering every failure path.
SA-8 requires application of engineering principles that include fail-secure design, reducing the likelihood the weakness is introduced.
SC-24 directly requires the system to fail to a known state that preserves security properties, structurally stopping fallback to a less-secure mode.
Boundary protection limits the network reach of server-initiated requests even if SSRF occurs.
Input validation directly stops untrusted URLs from being accepted and fetched without destination checks.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.
Vulnerability identification processes can discover and record SSRF flaws in web applications.
Least-privilege policy and enforcement directly counters the permissive-access fallback example in the CWE.
Network segmentation and egress controls can limit the damage from successful SSRF requests.
Hardened baselines and configuration management reduce the chance that error paths default to insecure settings.
Secure-development practices explicitly include designing error and failure handling to remain in a secure state.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Operational threat data describing SSRF campaigns can be used to tighten outbound-request allow-lists and detection rules before attackers exploit them.