---
id: "CVE-2026-129122"
page: "https://infrastack.ai/live/CVE-2026-129122"
kind: "vulnerability"
aliases: ["CVE-2026-129122"]
title: "C-Kermit: Telnet server can overflow client memory via environment variables"
severity: "high"
cvss: 7.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c-kermit", "linux", "package", "telnet", "unix"]
not_affected_if: ["no-telnet-use", "trusted-servers-only"]
published_at: "2026-11-13T17:17:29+00:00"
first_seen_at: "2026-11-13T17:48:00+00:00"
updated_at: "2026-11-13T17:48:48+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-129122", "first_seen_at": "2026-11-13T17:48:00+00:00"}]
exploit_sources: []
---

# C-Kermit: Telnet server can overflow client memory via environment variables

Link for people: https://infrastack.ai/live/CVE-2026-129122 (this .md is for agents)

C-Kermit 6.0.192 through versions before 11.1.515 has a buffer overflow in its Telnet NEW-ENVIRON handling. A malicious or man-in-the-middle Telnet server can send oversized variable names before authentication, corrupting stack and heap memory in the client.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `kermit` and check the version banner for a release earlier than `11.1.515`
- Check whether the Telnet client is used to connect to servers you do not fully control

## Fix

- C-Kermit: move to `11.1.515` or later (the fixed version named in the product range)

## Timeline

- 2026-11-13T17:48:00+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-129122

## Documents

- [advisory] Vendor advisory: github.com https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/c-kermit-6.0.192-before-11.1.515-buffer-overflow-via-telnet-new-environ-negotiation
- [fix] Patch: github.com https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f
- [fix] Patch: github.com https://github.com/OpenKermit/ckermit/commit/42cf6decb926f56d606a76262791aaf071955d25
- [fix] Release notes: github.com https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515

## From the sources

C-Kermit 6.0.192 before 11.1.515 contains a buffer overflow vulnerability in tn_snenv() in ckctel.c that allows malicious Telnet servers to corrupt client memory via crafted NEW-ENVIRON SEND subnegotiation. Malicious or machine-in-the-middle servers can send oversized variable names before authentication, overflowing a 16-byte stack buffer and a miscomputed heap buffer to corrupt stack and heap memory.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_