SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-77866
StatePUBLISHED
AssignerEEF
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-15 16:17:24 UTC
Updated2026-09-21 19:17:10 UTC
DescriptionServer-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.

Risk And Classification

Primary CVSS: v4.0 9 CRITICAL from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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:X

EPSS: 0.004600000 probability, percentile 0.391320000 (date 2026-09-22)

Problem Types: CWE-636 | CWE-918 | CWE-918 CWE-918 Server-Side Request Forgery (SSRF) | CWE-636 CWE-636 Not Failing Securely ('Failing Open')

VersionSourceTypeScoreSeverityVector
4.06b3ad84c-e1a6-4bf7-a703-f496b71e49dbSecondary9CRITICALCVSS: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/C...
4.0CNACVSS9CRITICALCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Confidentiality
High
Integrity
Low
Availability
None
Sub Conf.
High
Sub Integrity
Low
Sub Availability
None

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:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Slab Safeurl affected 0.1.0 * semver Not specified
CNA Slab Safeurl affected feabbd0a13f83028ab24b71710526e9da9841f70 * git Not specified

References

ReferenceSourceLinkTags
cna.erlef.org/cves/CVE-2026-77866.html 6b3ad84c-e1a6-4bf7-a703-f496b71e49db cna.erlef.org
osv.dev/vulnerability/EEF-CVE-2026-77866 6b3ad84c-e1a6-4bf7-a703-f496b71e49db osv.dev
github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9... 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Mathias Polligkeit (en)

CNA: Jonatan Männchen / EEF (en)

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