pageant crate CVE-2026-102820

Requires a local, co-located process on the same Windows host as the victim, and the victim must be running a russh-based SSH client that queries a Pageant agent via AgentClient::connect_pageant / query_pageant_direct (pageant crate before 0.2.3 / russh before v0.63.2). The attacker must impersonate the Pageant window to control the u32 response length written into the 8192-byte shared-memory mapping. Limiting factors: exploitation is local-only (no remote reach), depends on the client actually initiating a Pageant query, and requires winning the window-impersonation against the real Pageant; the memory-disclosure outcome is only conditional whereas the client crash is reliable.

This is a genuine but moderate-severity local availability issue, correctly scored around CVSS 6.2. The vendor vector CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H is internally consistent with the description: exploitation requires a LOCAL attacker process (AV:L), the impact is a reliable crash of the russh client (A:H), and the vector lists no confidentiality impact (C:N) even though the description notes a CONDITIONAL adjacent-memory disclosure - so an argument exists for C:L, a point where the vector slightly understates the read primitive. No EPSS score, KEV listing, or public POC was supplied, so exploitation status is: no public exploit identified at time of analysis. There is no signal conflict on attack vector (both the vector and description agree this is local-only, requiring a co-located process able to impersonate the Pageant window). The realistic priority is MEDIUM: it is a local DoS with conditional info-leak against a specific Rust SSH client configuration on Windows, not a remotely-reachable critical flaw. The presence of a clear upstream fix and confirming source diff raises confidence in the technical claim while the local-only vector and absence of exploitation evidence cap the urgency.

A malicious unprivileged process running on the same Windows host creates a window impersonating Pageant, then when a victim russh-based SSH client calls query_pageant_direct it returns a crafted u32 length (up to ~4 GiB) through the 8192-byte shared-memory mapping. MemoryMap::read trusts that length and copies beyond the mapped view, reliably crashing the SSH client and conditionally leaking adjacent committed process memory. No public exploit code was identified at time of analysis; exploitation is local-only and requires winning the Pageant-window impersonation.