# CVE-2026-83742: wstrncat() unsigned integer underflow leads to an off-by-one null write in wolfSSH on non-Windows platforms

> An authenticated attacker can cause a denial of service by triggering an integer underflow in wolfSSH that leads to a stack buffer overflow.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/AU:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 7 Oct 2026
- **Updated:** 7 Oct 2026
- **Also known as:** GHSA-4ff8-whrv-3wcm

## What is CVE-2026-83742?

CVE-2026-83742 is a medium-severity vulnerability in wolfSSL Inc. wolfSSH, published on 7 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Unsigned integer underflow in wstrncat() in src/port.c in wolfSSL wolfSSH from v1.4.11 through v1.5.0 on non-Windows platforms allows an authenticated remote attacker to write one out-of-bounds null byte past the end of a stack buffer by sending a crafted SFTP path. wolfSSH_RealPath() in src/ssh.c appends each path component with a remaining-size bound (outSz - curSz) rather than the full destination size, so once the accumulated path reaches half the output buffer the size_t computation n - strlen(s1) - 1 wraps to near SIZE_MAX. The strncat() call is then effectively unbounded and copies the whole component; when that component exactly fills the remainder of the buffer, its terminating null is written one byte past the end. The caller's own length check keeps the copied data inside the buffer, so the overflow is limited to that single null byte, which may corrupt an adjacent stack value and crash the process. Applications that call the public wolfSSH_RealPath() with an output buffer smaller than the input path are additionally exposed to an unbounded copy, because the word32 expression outSz - segSz in that length check also wraps.

Weakness: CWE-193 (Off-by-one Error), CWE-191 (Integer Underflow (Wrap or Wraparound)), CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-83742?

It affects 1 product.


Products: Wolfssh Wolfssh.

## How do I fix CVE-2026-83742?

No fix has been published for CVE-2026-83742 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-83742 being exploited?

There is no known exploitation of CVE-2026-83742 in the wild and no public exploit code.

## Other vulnerabilities in wolfSSL Inc. wolfSSH

- [CVE-2022-32073](https://insights.sbomify.com/CVE-2022-32073/): Integer overflow in n/a (critical 9.8)
- [CVE-2025-14942](https://insights.sbomify.com/CVE-2025-14942/): Authentication Bypass (critical 9.4)
- [CVE-2025-11625](https://insights.sbomify.com/CVE-2025-11625/): Host verification bypass and credential leak (critical 9.4)
- [CVE-2024-2873](https://insights.sbomify.com/CVE-2024-2873/): User authentication bypass in wolfSSH server (critical 9.1)
- [CVE-2026-16516](https://insights.sbomify.com/CVE-2026-16516/): wolfSSH ECDSA host key curve not validated against negotiated algorithm (critical 9.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-83742 and fix it if it is affected.

What it is: CVE-2026-83742 is a medium-severity vulnerability in wolfSSL Inc. wolfSSH, published on 7 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-83742 in the wild and no public exploit code.

Affected product: wolfSSL Inc. wolfSSH. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-83742/ (Markdown: https://insights.sbomify.com/CVE-2026-83742/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-83742
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-83742
- OSV: https://osv.dev/vulnerability/CVE-2026-83742

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-83742/
Summaries are generated and may contain mistakes; the official description above is the record.