{"id":"CVE-2026-77972","title":"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.\n\nValidation returns a verdict and not the addre…","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.\n\nValidation returns a verdict and not the addre…","severity":"critical","cvss":9,"cvssVector":"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"],"vendor":"Slab","product":"safeurl","affected":["safeurl >= 0.1.0 < *","slab/safeurl-elixir >= feabbd0a13f83028ab24b71710526e9da9841f70 < *"],"published":"2026-09-15","updated":"2026-09-21","sourceUpdated":"2026-09-21T19:17:11.153","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-77972","references":[{"url":"https://cna.erlef.org/cves/CVE-2026-77972.html","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-77972","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}],"tags":["nvd","cve.org"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-09-21T18:44:04.900610Z"},"cvssSource":"cna","epss":0.00317,"epssPercentile":0.2477,"ingestedAt":"2026-09-15T16:40:03.390Z","slug":"CVE-2026-77972","body":"## Overview\n\nTime-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.\n\nValidation 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.\n\nThis issue affects safeurl: from 0.1.0 onward.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":50,"depthScoreParts":{"impact":49.5,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}