# CVE-2026-84897 — wolfSSL Inc. wolfSSH

> As of 2026-10-07, CVE-2026-84897 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in wolfSSL Inc. wolfSSH, CVSS v4.0 6.9, EPSS 0.3% (20.9th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-84897, most recently “wolfSSH 1.6.0 patches 5 vulnerabilities incl. critical ECDSA host-key MITM (CVE-2026-16516) and Windows wolfSSHd auth-token reuse (CVE-2026-83540)”.

**Last updated:** 2026-10-07

## What is CVE-2026-84897?

src/internal.c in wolfSSL wolfSSH through 1.5.0 admits the server-to-client Diffie-Hellman group exchange messages SSH_MSG_KEX_DH_GEX_GROUP (31) and SSH_MSG_KEX_DH_GEX_REPLY (33) when a server receives them from an unauthenticated client. IsMessageAllowedServer() applies no direction check to the key exchange message range: when the peer is keying and no particular message is expected, which is the state a server is in for the whole window after it processes the client's KEXINIT because nothing sets handshake->expectMsgId there, the function falls out of its expectation branch without a verdict and reaches a numeric bound that admits every message id from 30 through 34. A client that negotiates diffie-hellman-group-exchange-sha256 and then sends message 31 makes the server run the client-side handler DoKexDhGexGroup(), which validates the attacker-supplied group with two 8-round Miller-Rabin primality tests, one on p and one on (p-1)/2, on a value of up to 8192 bits. The handler then returns success: the server stores the attacker's prime and generator, generates a Diffie-Hellman key pair in the attacker's group, and sends the client-role message SSH_MSG_KEX_DH_GEX_INIT (32) back to the attacker. Published RFC 3526 safe primes are the worst-case input and cost the attacker nothing to obtain. The primality validation was added in 1.5.0; versions from 1.2.0 through 1.4.22 admit the same message and enter the same client-role path without the primality cost. Message 33 is admitted as well, but on a server it is rejected before any cryptography because no public key check callback is registered, so it carries no comparable cost. Builds that define WOLFSSH_NO_DH_GEX_SHA256, which is implied by WOLFSSH_NO_DH or NO_SHA256, are unaffected.

The record classifies CVE-2026-84897 under weakness classes [CWE-372](https://cwe.mitre.org/data/definitions/372.html), [CWE-405](https://intel.threadlinqs.com/cwe/CWE-405), [CWE-400](https://intel.threadlinqs.com/cwe/CWE-400). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 3 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6.9 — Medium (derived from score) (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/AU:Y`)
- **EPSS (FIRST):** 0.3% probability of exploitation in the next 30 days, higher than 20.9% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-10-07

## Is CVE-2026-84897 being exploited?

It currently carries a trending score of 39 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [wolfSSL Inc.](https://intel.threadlinqs.com/vendors/wolfssl): wolfSSH

## How to fix CVE-2026-84897

No vendor patch reference has been recorded for CVE-2026-84897 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-84897

1 tracked threat in the Threadlinqs corpus references CVE-2026-84897, either in the campaign’s CVE list or as an indicator on the campaign record.

- [wolfSSH 1.6.0 patches 5 vulnerabilities incl. critical ECDSA host-key MITM (CVE-2026-16516) and Windows wolfSSHd auth-token reuse (CVE-2026-83540)](https://intel.threadlinqs.com/threat/TL-2026-3044) — CRITICAL · 2026-10-08

## Sources

Enriched from CVE.org, FIRST EPSS. Last verified by Threadlinqs on 2026-10-10.

**Vendor advisory and patch**

- [github.com — patch](https://github.com/wolfSSL/wolfssh/pull/1221)
- [github.com — patch (a472f1ee2b653f623d85ef2297321733f1dbfd22)](https://github.com/wolfSSL/wolfssh/commit/a472f1ee2b653f623d85ef2297321733f1dbfd22)

**Technical analysis**

- [rfc-editor.org — technical description](https://www.rfc-editor.org/rfc/rfc4419.html)
- [rfc-editor.org — technical description (rfc3526)](https://www.rfc-editor.org/rfc/rfc3526.html)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-84897
Full detection coverage and IOCs for threats exploiting CVE-2026-84897 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp