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CVE-2026-42189 high CVSS 7.5

Vulnerability in russh (CVE-2026-42189)

Summary

Vulnerability in russh (CVE-2026-42189). Risk of unauthorized operations or information disclosure. Exploitable via read_userauth_info_response. Mitigation: upgrade to 0.60.1 or later.

Original description

The description as published by the source.

Summary

A pre-authentication denial-of-service vulnerability exists in the server's keyboard-interactive authentication handler. A malicious client can crash any russh-based server that implements keyboard-interactive auth (e.g., for 2FA/TOTP) with a single malformed packet, requiring no credentials.

Vulnerability Details

In russh/src/server/encrypted.rs, the function read_userauth_info_response decodes a u32 count from the client's SSH_MSG_USERAUTH_INFO_RESPONSE and passes it directly to Vec::with_capacity():

let n = map_err!(u32::decode(r))?;

// Bound both allocation and iteration by remaining packet data to
// prevent a malicious client from causing a multi-GB allocation or
// billions of loop iterations with a crafted count.
// Each response needs at least 4 bytes (length prefix).
let max_responses = r.remaining_len().saturating_add(3) / 4;
let n = (n as usize).min(max_responses);
let mut responses = Vec::with_capacity(n);
for _ in 0..n {
    responses.push(Bytes::decode(r).ok())
}

An attacker can send n = 0x10000000 (268M) or larger in a minimal packet (~50 bytes after encryption). The server attempts to allocate n * ~24 bytes (size of Option) = ~6.4GB, causing an OOM crash.

Attack Flow

  1. Attacker connects via TCP, completes key exchange (no credentials needed -- this is the anonymous DH handshake, not authentication)
  2. Sends USERAUTH_REQUEST with method keyboard-interactive
  3. Server handler returns Auth::Partial with…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-42189 has been found in russh.
Attackers can target a specific entry point like read_userauth_info_response over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade russh to 0.60.1 or later.
If unsure, ask your IT team or search "russh CVE-2026-42189" on the vendor's site.

CVE-2026-42189 (russh) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: read_userauth_info_response / u32 / SSH_MSG_USERAUTH_INFO_RESPONSE / USERAUTH_REQUEST
Patched: 0.60.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-770) exists in russh. Attackers reach the vulnerable code path via read_userauth_info_response without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of russh. Attack surface: read_userauth_info_response / u32 / SSH_MSG_USERAUTH_INFO_RESPONSE / USERAUTH_REQUEST.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.60.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'russh' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'russh' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で russh を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade russh to 0.60.1

    ステージング環境で 0.60.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

rust russh
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.60.1"}]}]
crates.io russh
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.60.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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