CVE-2026-84381 in HTTPX2
Summary
by MITRE • 09/02/2026
HTTPX2 is a next generation HTTP client for Python. Prior to 2.10.0, httpcore2 fails to start TLS in src/httpcore2/httpcore2/_sync/socks_proxy.py and src/httpcore2/httpcore2/_async/socks_proxy.py when the remote origin uses wss through a SOCKS5 proxy because the TLS upgrade condition only recognizes https. HTTPX2 exposes the flaw through Client.websocket() and AsyncClient.websocket() from 2.6.0 through 2.9.1, so the opening handshake, query parameters, Authorization headers, cookies, and subsequent frames can cross the proxy path in plaintext without certificate verification. An attacker controlling or observing that path can read or modify traffic and impersonate the WebSocket server. This issue is fixed in httpcore2 2.10.0 and HTTPX2 2.10.0.
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Analysis
by VulDB Data Team • 09/02/2026
The vulnerability identified in HTTPX2 versions prior to 2.10.0 represents a critical failure in transport layer security when utilizing WebSocket Secure connections over SOCKS5 proxies. This flaw originates within the underlying httpcore2 library, specifically affecting both synchronous and asynchronous proxy handling modules located at src/httpcore2/_sync/socks_proxy.py and src/httpcore2/_async/socks_proxy.py respectively. The core technical defect lies in the logic governing TLS upgrades for WebSocket connections. When a client attempts to establish a secure connection using the wss scheme through a SOCKS5 proxy, the code incorrectly restricts the TLS upgrade condition to only recognize https endpoints. Consequently, when the remote origin specifies wss, the library fails to initiate the necessary Transport Layer Security handshake over the established SOCKS tunnel. This oversight results in the WebSocket opening handshake, along with all subsequent communication frames being transmitted in plaintext across the proxy path.
The operational impact of this vulnerability is severe due to the exposure of sensitive data and authentication mechanisms during transit. Because the TLS upgrade does not occur for wss connections routed through a SOCKS5 proxy, critical components such as query parameters, Authorization headers containing credentials or tokens, cookies, and application-level WebSocket frames are transmitted without encryption. Furthermore, since no certificate verification is performed in this plaintext state, there is no mechanism to validate the identity of the remote server. This lack of integrity checks allows an attacker who controls or observes the network path between the client and the SOCKS proxy to perform passive eavesdropping to harvest sensitive information or active man-in-the-middle attacks to modify traffic content dynamically. The ability to impersonate the WebSocket server further compromises trust, potentially leading to session hijacking or injection of malicious payloads into the application stream.
From a classification perspective, this vulnerability aligns with CWE-319 Cleartext Transmission of Authentication Information and CWE-295 Improper Certificate Validation. In terms of adversary tactics, it facilitates techniques associated with MITM under ATT&CK ID T1048 which involves encryption for evasion or interception, although in this case the failure is due to missing encryption rather than intentional obfuscation by an attacker. The flaw persists across HTTPX2 versions from 2.6.0 through 2.9.1 and affects both synchronous Client.websocket() and asynchronous AsyncClient.websocket() methods. To mitigate this risk, organizations must upgrade httpcore2 and HTTPX2 to version 2.10.0 or later where the TLS upgrade logic has been corrected to properly handle wss schemes over SOCKS5 proxies. Until such an update is applied, developers should avoid using WebSocket Secure connections through SOCKS5 proxies with these library versions or implement alternative secure routing mechanisms that ensure end-to-end encryption regardless of proxy type.