CVE-2026-107785

Crux Agent silently fails SKA preshared key rotation when SHA-512 peering is negotiated

Published Oct 9, 2026 CVSS 4.0 · 6.3 Medium EPSS < 1% KEV · Not listed
Description
Crux Agent from 1.9.0 before 2.0.3 uses the full SKA bilocation key as the WireGuard preshared key. When a peering session negotiates use of SHA-512, the key produced is 64 bytes instead of the 32 bytes WireGuard requires. The agent does not validate this size; instead it attempts to use the `wg set` command to update the live tunnel, and write the invalid key to the WireGuard configuration file. The update fails, so the live tunnel keeps using its previous preshared key until the tunnel is shut down. The tunnel will fail to start when restarted.



For a peer which has never successfully negotiated a 32-byte bilocation key in a Crux C2 organization which has the "Enforce SKA Use" setting turned off, no preshared key will be set for the tunnel. Therefore, an attacker who is able to intercept and store the peer's traffic, and has access (or will have access) to a cryptographically relevant quantum computer, will be able to decrypt the tunnel.

Remediation

Vendor Solution

Upgrade to Crux Agent 2.0.3 or later, which truncates the SKA key to the 32 bytes WireGuard requires. As a workaround, remove any custom settings for "Hash Function" in the agent's configuration (so as to use the default SHA-256 hash function).

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Sirius Computer
Sirius Computer crux Agent
Vendors & Products Sirius Computer
Sirius Computer crux Agent
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description Crux Agent from 1.9.0 before 2.0.3 uses the full SKA bilocation key as the WireGuard preshared key. When a peering session negotiates use of SHA-512, the key produced is 64 bytes instead of the 32 bytes WireGuard requires. The agent does not validate this size; instead it attempts to use the `wg set` command to update the live tunnel, and write the invalid key to the WireGuard configuration file. The update fails, so the live tunnel keeps using its previous preshared key until the tunnel is shut down. The tunnel will fail to start when restarted. For a peer which has never successfully negotiated a 32-byte bilocation key in a Crux C2 organization which has the "Enforce SKA Use" setting turned off, no preshared key will be set for the tunnel. Therefore, an attacker who is able to intercept and store the peer's traffic, and has access (or will have access) to a cryptographically relevant quantum computer, will be able to decrypt the tunnel.
Title Crux Agent silently fails SKA preshared key rotation when SHA-512 peering is negotiated
Weaknesses CWE-252
CWE-325
CWE-394
References
Metrics cvssV4_0

{'score': 6.3, 'vector': 'CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N/E:U/S:N/AU:Y/R:A/V:C/RE:L/U:Amber'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
sirius
Published
Updated
Oct 9, 2026, 4:46 PM
Reserved
Oct 8, 2026, 8:13 PM
Status
Deferred
Published
Oct 9, 2026, 2:17 PM
Modified
Oct 9, 2026, 5:16 PM