CVE-2026-82533: Reliance on Untrusted Inputs in a Security Decision in DeepSeek DeepSeek Harness

CVE-2026-82533 is an authentication bypass vulnerability in DeepSeek Harness prior to version 0.1.2-alpha.1. The vulnerability arises because the software accepts a client-supplied loopback Host header to authenticate access to its local HTTP agent-control API, rather than verifying the true origin of the TCP connection. This allows an attacker with local confined process access to bypass sandbox restrictions and escalate privileges. Additionally, if the API port is exposed externally through mechanisms such as SSH tunnels, forward or reverse proxies, remote attackers can exploit the same flaw to create sessions, execute arbitrary commands, and steal stored conversation data without needing credentials.

The vulnerability allows unauthenticated attackers to bypass authentication controls on the local HTTP agent-control API. Locally, this can lead to sandbox escape, privilege escalation to unconfined execution, and disabling of approval prompts. Remotely, if the API port is exposed, attackers can fully compromise the system by creating sessions, executing arbitrary commands, and exfiltrating sensitive data such as conversation transcripts. The CVSS 4.0 score of 9.4 reflects the critical severity and the high impact on confidentiality, integrity, and availability.

A fix is available in DeepSeek Harness version 0.1.2-alpha.1 and later. Users should upgrade to version 0.1.2-alpha.1 or newer to remediate this vulnerability. Until patched, ensure that the local HTTP agent-control API port is not exposed externally via tunnels, SSH forwarding, or proxies to reduce remote attack risk.