VulnerabilityPublished 13 Nov 2026

CVE-2026-128087: russh kex_done · Shared-secret callback runs before server host-key verification

Affects russhSource GCVE Database

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Authoritative record:CVE-2026-128087· Low 3.7

Not known to be exploited · CVSS 3.7 Low : upgrade to 0.65.1 when convenient.

Data as of 13 Nov 2026, 20:18 UTC

CVSS 3.1 base score

3.7Low

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.1	3.7

Patch: Available – fixed in 0.65.1

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade russh to 0.65.1.

Affected software

Product	Affected	Fixed in
crates.iorussh	Affected >=0.55.0 <0.65.1	Fixed in 0.65.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fixed version of russh is available in 0.65.1 that ensures check_server_key() is called before kex_done() during the initial key exchange, preventing untrusted servers from triggering the callback with the shared secret. Users should upgrade to russh version 0.65.1 or later to remediate this issue. No other mitigation is required as the vulnerability is addressed by this official fix.

Description

A vulnerability in the russh SSH client library allows a malicious SSH server, whose host key is ultimately rejected, to trigger the client's kex_done() callback with the raw key-exchange shared secret before server host-key verification occurs. This callback is intended for protocol bridging such as VPN-over-SSH or secondary encrypted channels. Because kex_done() runs before check_server_key(), an untrusted server can cause application-defined actions based on the shared secret even though the connection is later rejected.

Impact

The vulnerability allows a malicious SSH server to cause the russh client to execute application-defined secondary-channel actions using the shared secret before the server's host key is verified and rejected. This could lead to exposure of cryptographic material or initialization of unauthorized secondary encrypted channels despite the server being untrusted. However, it does not allow bypassing the host key verification itself or direct compromise of the SSH session. The impact is limited to potential misuse of the shared secret in the kex_done() callback prior to trust verification.

Summary

In russh versions from 0.55.0 through 0.65.0, the client::Handler::kex_done() callback is invoked immediately after the server proves possession of its host key during the initial key exchange, but before the client application verifies the server's host key via check_server_key(). This ordering allows a malicious SSH server with an untrusted host key to cause the client to execute kex_done() with the shared secret, potentially enabling secondary-channel initialization or other externally visible actions before the server key is rejected. The flaw was introduced in commit 500bef1eccc1c48ac674e2a262aa7887777431eb and is fixed in version 0.65.1. The vulnerability has a CVSS 3.1 score of 3.7 (low severity) and does not allow direct compromise but may lead to unintended protocol bridging actions with untrusted servers.

CWE-696Incorrect Behavior Order (opens in a new tab)
Class weakness
The product performs multiple related behaviors, but the behaviors are performed in the wrong order in ways that may produce resultant weaknesses.
Attack patterns
Padding Oracle Crypto Attack (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 13 Nov 2026, 20:18 UTC

WeaknessesCWE-696, CWE-863

Technical details

References

Community reviews

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