# CVE-2026-77972

## Summary

- **CVE ID:** CVE-2026-77972
- **Severity:** CRITICAL
- **CVSS Score:** 9 (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)
- **CWE:** CWE-367
- **Published:** Sep 15, 2026
- **Last Modified:** Sep 15, 2026

## 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

- Slab — safeurl (0.1.0)
- Slab — safeurl (feabbd0a13f83028ab24b71710526e9da9841f70)

## References

- [CNA](https://cna.erlef.org/cves/CVE-2026-77972.html)
- [CNA](https://osv.dev/vulnerability/EEF-CVE-2026-77972)
- [CNA](https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.32%
- **EPSS Percentile:** 24.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._