Vulnerability · Published Sep 15, 2026 · Assigned by EEF

CVE-2026-77972safeurl validated address is not bound to the request, allowing DNS rebinding

Critical 9.0

In plain English

A critical-severity security flaw in safeurl from Slab. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities).

Severity (CVSS 4.0)9.0Critical

Exploit odds (30 days)0.3%top 73.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Time-of-check Time-of-use (TOCTOU) Race Condition in Slab safeurl allows an attacker who controls a hostname's DNS responses to reach internal network destinations that validation rejected. Validation returns a verdict and not the address it approved, so the HTTP clients the library ships receive the original hostname and resolve it a second time when the request is made. An attacker who controls the authoritative DNS for a name can answer the first lookup with a permitted address and the second with a blocked one, and the request then reaches a destination validation never approved. The same window opens without an attacker whenever a name legitimately resolves to different addresses across lookups, such as short record lifetimes or rotation between several addresses. This issue affects safeurl: from 0.1.0 onward.

Affected products (as reported)

Vendor	Product	Versions
Slab	safeurl	0.1.0 – before *
Slab	safeurl	feabbd0a13f83028ab24b71710526e9da9841f70 – before *

Weakness: CWE-367 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N

References

EEF CNA record for CVE-2026-77972 related, third-party-advisory
OSV record EEF-CVE-2026-77972 related
Introducing commit feabbd0 in slab/safeurl-elixir related