2FAuth: Authenticated SSRF via DNS rebinding in the otpauth image= icon fetch (validate-then-fetch TOCTOU)
- Exploited
- No known exploitation
- Fix
- Fixed in 8.0.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 8.0.0.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 9/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
2FAuth, a web app for managing two-factor authentication accounts and generating security codes, can be abused by a logged-in user to make the server request internal resources, such as loopback services, private-network hosts, or cloud metadata endpoints, by using DNS rebinding to bypass its address checks when external otpauth image fetching is enabled. The attack can be launched remotely by any authenticated user without action from anyone else, and it can expose sensitive information from those internal endpoints.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
2FAuth 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure3/25Reachable over the network · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity5.9/10CVSS 5.9
- No patch0/5No signal
What would change the score
- Would score about 64 if added to CISA KEV
- Would score about 59 if CISA's SSVC rates exploitation active
- Would score about 28 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 8.0.0.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- Bubka 2FAuth
fixed in 8.0.0
Evidence 3
- Advisory
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-63440
Is CVE-2026-63440 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-63440?
2FAuth: before 8.0.0.Source: cve.now feed data
How do I fix CVE-2026-63440?
Upgrade to a fixed version: 8.0.0.Source: cve.now feed data