2FAuth: Authenticated SSRF via DNS rebinding in the otpauth image= icon fetch (validate-then-fetch TOCTOU)

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63440
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-06 21:17:10 UTC
Updated2026-11-12 22:11:01 UTC
Description2FAuth is a web app to manage Two-Factor Authentication (2FA) accounts and generate their security codes. Prior to 8.0.0, the otpauth image-fetch path validates a hostname through ValidatesUrls::isExternalHost() and then lets IconService::storeRemoteImage() resolve the same hostname again for the HTTP request. When external otpauth image fetching is enabled, an authenticated user controlling low-TTL authoritative DNS can return a public address during validation and an internal address during the later connection, bypassing the private-address deny list to reach loopback, private-network, link-local, or cloud metadata endpoints. This issue is fixed in version 8.0.0.

Risk And Classification

Primary CVSS: v3.1 5.9 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N

EPSS: 0.002020000 probability, percentile 0.102690000 (date 2026-11-10)

Problem Types: CWE-367 | CWE-918 | CWE-367 CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition | CWE-918 CWE-918: Server-Side Request Forgery (SSRF)

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
3.1CNADECLARED5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Bubka 2FAuth affected < 8.0.0 Not specified

References

ReferenceSourceLinkTags
github.com/Bubka/2FAuth/security/advisories/GHSA-22mh-gmrh-gpwg 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/Bubka/2FAuth/commit/52e9db94f2da2a6231d77c49537d6d88ce948ee1 [email protected] github.com
github.com/Bubka/2FAuth/releases/tag/v8.0.0 [email protected] github.com
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