CVE-2026-116774VulnerabilityPublished 30 Oct 2026

russh: peer-declared zero maximum packet size permanently stalls channel writes (silent AsyncWrite hang)

Affects russhSource GCVE Database

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Authoritative record:CVE-2026-116774· Medium 4.3

Not known to be exploited · CVSS 4.3 Medium : upgrade to 0.65 when convenient.

Data as of 31 Oct 2026, 02:06 UTC

CVSS 3.1 base score

4.3Medium

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	4.3

Patch: Available – fixed in 0.65

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

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

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: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
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: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Oct 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 30 Oct 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.

Affected software

Product	Affected	Fixed in
crates.iorussh	Affected >=0.60.0 <0.65	Fixed in 0.65

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AI-suggested

A fix is available in russh version 0.65 that properly validates and rejects a zero maximum packet size in all write paths, including AsyncWrite. Users should upgrade to version 0.65 or later to remediate this issue. No other mitigation is required as the vulnerability is addressed by this official fix.

Description

A vulnerability in russh versions 0.60.0 up to but not including 0.65 allows a peer to advertise a maximum packet size of zero in channel-open messages. This causes the AsyncWrite path to stall indefinitely because the write operation never completes or errors, leading to a silent hang of the application task. The issue arises from lack of validation of the peer-declared maximum packet size and inconsistent handling in the AsyncWrite code path. This can be exploited by an authenticated client against a server or by a malicious server against a client to cause a denial of service by hanging write operations.

Impact

An authenticated client can exploit this vulnerability to cause a denial of service on a russh server by opening a session channel with a maximum packet size of zero, causing server write operations on that channel to hang indefinitely. Similarly, a malicious server can cause a russh client to hang writes by confirming a channel with a zero maximum packet size. The hang is silent with no error reported, leading to stranded resources and potential service disruption. The CVSS score is 4.3 (medium severity) reflecting a remote, low-complexity denial of service with no confidentiality or integrity impact.

Summary

The russh crate accepts a peer-declared maximum packet size of zero in channel-open messages without validation. This zero value is used verbatim in the channel write state, capping outgoing data chunk sizes to zero. In the AsyncWrite code path, this results in every write future remaining pending indefinitely because the writable size is always zero and no event can increase it. Other write paths treat a zero max packet size as an error, but AsyncWrite lacks this guard, violating the crate's invariant. This leads to a permanent stall of channel writes without error or completion, causing application tasks to hang silently. The vulnerability affects russh versions >=0.60.0 and <0.65 and was fixed in version 0.65.

CWE-400Uncontrolled Resource Consumption (opens in a new tab)
Class weaknessLikelihood of exploit: High
The product does not properly control the allocation and maintenance of a limited resource.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place.
Architecture and Design
Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or; uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed.
Architecture and Design
Ensure that protocols have specific limits of scale placed on them.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Regular Expression Exponential Blowup (opens in a new tab)
Sustained Client Engagement (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-835Loop with Unreachable Exit Condition (Infinite Loop) (opens in a new tab)
Base weakness
The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 31 Oct 2026, 02:06 UTC

WeaknessesCWE-400, CWE-835

Technical details

References

Community reviews

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