CVE-2026-77972
safeurl validated address is not bound to the request, allowing DNS rebinding
- State
- Published
- Severity
- 9.0 Critical
- Published
- Sep 15, 2026
- Updated
- Sep 21, 2026
- Reserved
- Aug 24, 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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.0 Critical | 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 | EEF |
Weaknesses
- CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition
Affected Products
| Product | Versions |
|---|---|
safeurlSlab |
|
safeurlSlab |
|
References
- EEF CNA record for CVE-2026-77972relatedthird-party-advisory
- OSV record EEF-CVE-2026-77972related
- Introducing commit feabbd0 in slab/safeurl-elixirrelated
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