Is CVE-2026-77866 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-77866 being exploited in the wild.

How severe is CVE-2026-77866?

Informational severity, published 15 September 2026.

Is there a fix for CVE-2026-77866?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-77866 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-77866?

Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-77866: Slab safeurl SSRF via IPv6 and blocklist bypass

CVE-2026-77866 · Severity: info · Published 2026-09-15

Slab safeurl is a library used to validate and restrict HTTP requests to prevent attacks on internal network resources. A flaw in its validation logic allows attackers to bypass blocklists by using IPv6 addresses or alternative hostname formats, potentially reaching internal systems that should be blocked—such as cloud metadata endpoints or internal databases.

Quick answers

Is CVE-2026-77866 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-77866 being exploited in the wild.
How severe is CVE-2026-77866?: Informational severity, published 15 September 2026.
Which products and versions are affected?: Slab safeurl 0.1.0 and later.
Is there a fix for CVE-2026-77866?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-77866 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-77866?: Check whether anything you run is named in the advisory. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a Server-Side Request Forgery (SSRF) bypass in Slab safeurl's URL validation logic. The library only matches blocklist entries and reserved IP ranges against IPv4 addresses; IPv6 addresses and hostnames that resolve to no IPv4 address bypass the checks entirely. An attacker who controls a validated URL can craft requests using IPv6 notation or alternative address formats that resolve to internal destinations the blocklist is meant to prevent. This affects all deployments using blocklist-based filtering (allowlist deployments are unaffected since unmatched addresses are rejected). The vulnerability affects safeurl 0.1.0 and later; patch status is unknown.

Affected products

Slab safeurl 0.1.0 and later

Timeline

2026-09-15: published

References

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