wolfSSH SSH client accepts unsolicited forwarded-tcpip channel opens without an authorization check

published 2026-10-07 33 d ago modified 2026-10-13 26 d ago also EUVD-2026-94162

cvss: 9.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 23%
public exploits: 0; none known

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.

Patch / fix

fixed in 1 distros 1 links 3

wolfSSL Inc. wolfSSH 1.6.0

wolfssh Alpine 3.24 1.6.0-r0

alpine advisories ALPINE-CVE-2026-81535

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

github.com/wolfSSL/wolfssh@616eb68 commit
github.com/wolfSSL/wolfssh@e396a0a commit
github.com/wolfSSL/wolfssh@79a7f29 commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 32 d ago (2026-10-07)

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	6.3	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
CNA	4.0	6.3	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD	3.1	9.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

wolfSSL Inc. wolfSSH

Classification

Weakness

CWE-862 Missing Authorization
CWE-863 Incorrect Authorization

References

Sources

CVE List CVE-2026-81535
NVD CVE-2026-81535

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary