vulnerability / NVI-00018280 / Revision 1
Russh: Unchecked keyboard-interactive prompt count in client auth path
GitHub lists this reviewed advisory for russh. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.5 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
russh
source listed>= 0.37.0, < 0.61.0
### Summary In the `russh` client keyboard-interactive authentication path, a malicious SSH server could send a `USERAUTH_INFO_REQUEST` with an attacker-controlled prompt count, and the client would use that raw count directly in `Vec::with_capacity(...)` before validating that enough prompt data was actually present in the packet. This is a client-side denial-of-service / resource-exhaustion issue on the keyboard-interactive auth path. ### Details The vulnerable code path is in: - `russh/src/client/encrypted.rs` When the client is in `CurrentRequest::KeyboardInteractive` state and receives `SSH_MSG_USERAUTH_INFO_REQUEST`, it parses: 1. `name` 2. `instructions` 3. `language tag` 4. `n_prompts` Before the fix, the code then did: ```rust let n_prompts = map_err!(u32::decode(&mut r))?; let mut prompts = Vec::with_capacity(n_prompts.try_into().unwrap_or(0)); ``` That means a malicious server could advertise an enormous `n_prompts` value even if the packet contained no prompt bodies at all. The fix rejects inconsistent prompt counts before allocating: ```rust let n_prompts = map_err!(u32::decode(&mut r))?; let max_prompts = r.remaining_len() / 5; let n_prompts = n_prompts as u
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-g9g7-5cgw-6v28 ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.