CVE-2026-77972
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
Summary
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 Software
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| Slab | safeurl | 0.1.0 < * | affected |
| Slab | safeurl | feabbd0a13f83028ab24b71710526e9da9841f70 < * | affected |
Weaknesses
- CWE-367: CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
References
- https://cna.erlef.org/cves/CVE-2026-77972.html
- https://osv.dev/vulnerability/EEF-CVE-2026-77972
- https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70
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