EUVD-2026-42399Severity by source
AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Attacker controls the SSH server but the victim must initiate the SCP transfer (UI:R); arbitrary file write yields I:H and A:H, with no data disclosure (C:N).
Primary rating from Vendor (github).
CVSS VectorVendor: github
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Lifecycle Timeline
2DescriptionCVE.org
AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Prior to 2.23.1, a malicious SSH server can write arbitrary files on the asyncssh SCP client's filesystem by sending filenames containing ../ traversal sequences because _parse_cd_args in scp.py returns server-provided names verbatim and _recv_files joins them to the destination path without enforcing the target directory boundary. This issue is fixed in version 2.23.1.
Articles & Coverage 1
AnalysisAI
Arbitrary file write in the AsyncSSH Python library (versions prior to 2.23.1) allows a malicious or compromised SSH server to plant files anywhere on an SCP client's filesystem when a user initiates a file-copy operation against it. Because the SCP client trusts server-supplied filenames verbatim, a hostile server can return names containing ../ sequences to escape the intended download directory, enabling code execution or system tampering. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the victim to initiate an AsyncSSH SCP client download (receive/copy-from) against an attacker-controlled or compromised SSH server (UI:R) - the attacker must be positioned as the SCP server, not merely on the network. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score is 8.1 (High) with vector AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H - network reachable, low complexity, no privileges required, but user interaction is required (the victim must initiate an SCP transfer to the attacker-controlled server). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker stands up or compromises an SSH server and lures a victim into running an AsyncSSH-based SCP client to download files from it (for example a backup, sync, or automation job). During the transfer the server returns filenames like '../../../../home/user/.ssh/authorized_keys' or '../../etc/cron.d/evil', and the unpatched client writes them outside the intended directory. … |
| Remediation | Vendor-released patch: upgrade AsyncSSH to version 2.23.1 or later, which enforces the destination directory boundary when reconstructing received filenames (fix commit d730803b8e4e94c20c7580d90f94d1e05f9f58de; release https://github.com/ronf/asyncssh/releases/tag/v2.23.1). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: audit all internal applications and dependencies for AsyncSSH usage and identify affected versions. …
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External POC / Exploit Code
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