CVE-2026-81535

Undergoing Analysis Undergoing Analysis - In Progress

BaseFortify

Publication date: 2026-10-07

Last updated on: 2026-10-13

Assigner: wolfSSL Inc.

Description

In wolfSSH through 1.5.0 built with --enable-fwd, DoChannelOpen() in src/internal.c gates only direct-tcpip channel opens with the forwarding policy callback. forwarded-tcpip opens are admitted without an authorization check and are not capped in number, allowing a malicious SSH peer to make an endpoint allocate unbounded per-channel buffers for forwarding channels the application never authorized. A client also does not check a forwarded-tcpip open against the forwards it registered with a tcpip-forward request, as RFC 4254 section 7.2 requires, so a malicious server can open forwarding channels for addresses and ports the client never asked it to forward.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-10-07

Last Modified

2026-10-13

Generated

2026-10-19

AI Q&A

2026-10-07

EPSS Evaluated

2026-10-18

NVD

CVE-2026-81535

EUVD

EUVD-2026-94162

Affected Vendors & Products

Vendor	Product	Version / Range
wolfssh	wolfssh	to 1.6.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-863	The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
CWE-862	The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

Attack-Flow Graph

Executive Summary

This vulnerability in wolfSSH through 1.5.0 allows unauthorized forwarding of TCP/IP channels. When built with --enable-fwd, the system fails to properly validate forwarded-tcpip channel opens, letting malicious peers create unbounded per-channel buffers without authorization checks. Clients also don't verify forwarded-tcpip opens against registered forwards as required by RFC 4254 section 7.2.

Detection Guidance

Check if your wolfSSH version is 1.5.0 or earlier. Run 'wolfssh --version' to verify. Inspect SSH logs for unauthorized forwarded-tcpip channel opens or mismatches between client forwards and server responses. Use network monitoring tools to detect unexpected TCP forwarding attempts.

Impact Analysis

An attacker could exploit this to make the system allocate excessive memory for unauthorized forwarding channels, potentially causing denial-of-service or resource exhaustion. It may also allow unauthorized network access through improperly validated forwarding requests.

Compliance Impact

This vulnerability could impact compliance with GDPR and HIPAA by allowing unauthorized forwarding of network traffic through SSH channels. Improper validation of forwarded-tcpip channels may lead to unauthorized data exfiltration or access, violating data protection requirements under these regulations.

Mitigation Strategies

Upgrade wolfSSH to a patched version. Disable --enable-fwd if not needed. Implement strict validation for forwarded-tcpip channels. Ensure client-server forward matches are enforced per RFC 4254 section 7.2. Monitor logs for unauthorized forwarding attempts.

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