CVE-2026-77972

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-09-15 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-21 19:17 UTC Last updatedMost recent change to the record

Details

Published

2026-09-15 16:17 UTC

Last modified

2026-09-21 19:17 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-367

Record status

Awaiting Analysis

Attack profile CVSS 4.0 · 9.0

Attack vector

Network

Complexity

High

Attack requirements

Present

Privileges needed

None

User interaction

None

Confidentiality

High

Integrity

Low

Availability

None