HighCVE-2026-129122

C-Kermit 6.0.192 before 11.1.515 Buffer Overflow via Telnet NEW-ENVIRON Negotiation (CVE-2026-129122)

Published 13.11.2026Last modified 13.11.2026Sources: OSV, CVE.org, EUVD

What is affected, what to do

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.

Update OpenKermit C-Kermit to version 11.1.515.

Affected: OpenKermit C-Kermit lt 6.0.192..11.1.515
Fixed in: OpenKermit C-Kermit 11.1.515

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

7.7

XIEM Effective CVSS

Highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v4

7.5

CVSS v3

Severity High on the scale from 0 to 10.

Source: OSV, CVE.org, EUVD

—

EPSS score

No value is available for this vulnerability.

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 68.50 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 7.7 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.5
CVSS v4 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 7.7
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 13.11.2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-787

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Source: OSV (Open Source Vulnerabilities), NVD (NIST), ENISA EUVD, cvelistv5, CVE.org (MITRE)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
OpenKermit	C-Kermit	`6.0.192 – < 11.1.515`	`11.1.515`

Vendors and products

Openkermit C-kermit

Weakness classes (CWE)

CWE-787Out-of-bounds Write
Base
The product writes data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-787

References & sources

github.comGitHub Security Advisory (GHSA-c5px-7h4c-gj8p)euvd, Vendor advisory, advisory
github.comOpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc…euvd, Patch, fix
github.comOpenKermit/ckermit/commit/42cf6decb926f56d606a76262791aaf071955…euvd, Patch
github.comC-Kermit v11.1.515 Release Noteseuvd, Release notes, advisory
github.comOpenKermit/ckermit/blob/v11.0.514/ckctel.ceuvd, Technical description
vulncheck.comVulnCheck Advisory: C-Kermit 6.0.192 before 11.1.515 Buffer Overflow via Telnet NEW-ENVIRON Negotiationeuvd, Third-party advisory
NVD (NIST)vuln/detail/CVE-2026-129122euvd
github.comCVEProject/cvelistV5/tree/main/cves/2026/129xxx/CVE-2026-129123…advisory
github.comOpenKermit/ckermit/blob/v11.0.514/ckcftp.carticle
github.comOpenKermit/ckermit/commit/bec28a4d544031fa07a07aacba3df5dd1202e…fix
NVD (NIST)vuln/detail/CVE-2026-129123advisory
vulncheck.comadvisories/c-kermit-8.0.200-before-11.1.515-ftp-client-buffer-o…advisory
github.comCVEProject/cvelistV5/tree/main/cves/2026/129xxx/CVE-2026-129124…advisory
github.comOpenKermit/ckermit/blob/v11.0.514/ckcpro.warticle
github.comOpenKermit/ckermit/commit/29c4bfbe12d685f93668350c24291e562029f…fix
NVD (NIST)vuln/detail/CVE-2026-129124advisory
vulncheck.comadvisories/c-kermit-before-11.1.515-os-command-injection-via-re…advisory
github.comCVEProject/cvelistV5/tree/main/cves/2026/129xxx/CVE-2026-129125…advisory
github.comOpenKermit/ckermit/blob/v11.0.514/ckcpro.warticle
github.comOpenKermit/ckermit/commit/85ef1da670cee132ea2d8e4eb759bab310ff7…fix

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

13.11.2026ReceivedVulnCheck

CVSS V4.0: AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS V3.1: AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Weakness type: CWE-787

Description added or changed

New references:

and 2 more references

Show 11 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	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.
CVSS	added	—	AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/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
CVSS	added	—	AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness type (CWE)	added	—	CWE-787
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/129xxx/CVE-2026-129122.json">CVE-2026-129122</a>
Reference	added	—	https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckctel.c#L5622
Reference	added	—	https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f
Reference	added	—	https://github.com/OpenKermit/ckermit/commit/42cf6decb926f56d606a76262791aaf071955d25
Reference	added	—	https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
Reference	added	—	https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p
Reference	added	—	https://www.vulncheck.com/advisories/c-kermit-6.0.192-before-11.1.515-buffer-overflow-via-telnet-new-environ-negotiation

Source identifier: disclosure@vulncheck.com

Embed badge

Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

<a href="https://intel.neosec.eu/en/cve/CVE-2026-129122"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-129122.svg?lang=en" alt="CVE-2026-129122 – NEOSEC Intel" height="20"></a>