# CVE-2026-84897: wolfSSL wolfSSH Diffie-Hellman group exchange message handling bypass

Source: https://junglewise.ai/threats/cve-2026-84897-src-internal-c-in-wolfssl-wolfssh-through-1-5-0-admits-the-server  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-07. Updated: 2026-10-07  
License: CC BY 4.0 with a link back

CVE-2026-84897 · Severity: info · Published 2026-10-07

wolfSSL wolfSSH is an SSH library used in embedded systems and applications. A flaw in message validation allows an unauthenticated attacker to send server-side key exchange messages to a server, causing it to process them as if they came from the client. This forces the server to perform expensive primality validation on attacker-controlled cryptographic parameters, enabling denial-of-service attacks on SSH servers using this library.

Technologies: [Wolfssl wolfSSH](https://junglewise.ai/threats/technologies/wolfssl-wolfssh). Vendors: [Wolfssl](https://junglewise.ai/threats/vendors/wolfssl).

## Quick answers

**Is CVE-2026-84897 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84897 being exploited in the wild.

**How severe is CVE-2026-84897?** Informational severity, published 7 October 2026.

**Which products and versions are affected?** Wolfssl wolfSSH through 1.5.0.

**Is there a fix for CVE-2026-84897?** No fixed version is recorded yet. Disable Diffie-Hellman group exchange support by defining WOLFSSH_NO_DH_GEX_SHA256 at compile time. Builds that define WOLFSSH_NO_DH or NO_SHA256 are unaffected. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-84897 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-84897?** Check whether you run Wolfssl wolfSSH at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix


Disable Diffie-Hellman group exchange support by defining WOLFSSH_NO_DH_GEX_SHA256 at compile time. Builds that define WOLFSSH_NO_DH or NO_SHA256 are unaffected.

## Technical details

The IsMessageAllowedServer() function in src/internal.c fails to enforce directional checks on SSH key exchange messages SSH_MSG_KEX_DH_GEX_GROUP (31) and SSH_MSG_KEX_DH_GEX_REPLY (33) during the Diffie-Hellman group exchange negotiation. An unauthenticated client can send these server-to-client messages before authentication; the server incorrectly invokes the client-side handler DoKexDhGexGroup(), which validates the attacker-supplied prime using two 8-round Miller-Rabin tests on values up to 8192 bits. This allows a remote attacker to cause high CPU consumption and deny service.

## Affected products

- wolfSSL wolfSSH through 1.5.0

## Related threats

- [wolfSSL wolfSSH unsigned integer underflow in wstrncat()](https://junglewise.ai/threats/cve-2026-83742-unsigned-integer-underflow-in-wstrncat-in-src-port-c-in-wolfssl)
- [wolfSSL wolfSSHd Windows logon token release-of-resource vulnerability](https://junglewise.ai/threats/cve-2026-83540-when-password-or-public-key-authentication-is-used-with-the)
- [wolfSSH forwarded-tcpip channel authorization bypass](https://junglewise.ai/threats/cve-2026-81535-in-wolfssh-through-1-5-0-built-with-enable-fwd-dochannelopen-in)
- [wolfSSH ECDSA curve substitution in host key parsing](https://junglewise.ai/threats/cve-2026-16516-wolfssh-does-not-validate-that-the-ecdsa-curve-identifier-in-a)