CVE-2026-44726
Published: 23 June 2026
Summary
CVE-2026-44726 is a high-severity Cleartext Transmission of Sensitive Information (CWE-319) vulnerability in Deno Deno. Its CVSS base score is 7.4 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Adversary-in-the-Middle (T1557); ranked at the 3.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-38548
Vulnerability details
Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.0.0 until 2.7.8, a flaw in Deno's Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and…
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the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted. A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected. This vulnerability is fixed in 2.7.8.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability enables network-positioned attacker to force plaintext transmission of application data (by triggering failed address-family attempt) and observe/tamper with it, directly facilitating Adversary-in-the-Middle.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Role-based training covers secure transmission methods, mitigating cleartext transmission of sensitive data.
By requiring documented security controls for information exchanges, the control reduces the risk of cleartext transmission of sensitive data.
Mapping transmission actions in data flows helps prevent cleartext transmission of sensitive information.
Settings can enforce secure transmission protocols to prevent cleartext transmission of sensitive data.
Policy addresses secure transport and handling of media to avoid cleartext transmission of sensitive information.
Enforces safeguards against cleartext transmission of CUI when data leaves organizational boundaries to external systems.
Explicit controls and continuous oversight on external system services prevent cleartext transmission of sensitive information over provider-managed channels.
Key-establishment procedures specify secure distribution channels that preclude cleartext transmission of key material.