SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts (CVE-2026-77866) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-77866

SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts

Answer in brief

CVE-2026-77866 records a Unknown severity vulnerability in SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts. The current sources do not mark it as known exploited. The current feed maps Slab/safeurl (generic), Slab/safeurl (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 15, 2026Updated Sep 15, 2026Source checked Sep 15, 2026First seen by HOL Sep 15, 2026Material review Sep 15, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Slab/safeurl (generic), Slab/safeurl (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Slab/safeurlgeneric	>=0.1.0 <*	*
Slab/safeurlgeneric	>=feabbd0a13f83028ab24b71710526e9da9841f70 <*	*

Recommended response

Check inventory. Check lockfiles and deployed manifests for Slab/safeurl, Slab/safeurl.
Review the reported fix. Update Slab/safeurl to *; Slab/safeurl to * if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 15, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.