CriticalCVE-2026-129126

C-Kermit before 11.1.515 Heap Buffer Overflow via putsrv() Packet Decoding (CVE-2026-129126)

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

What is affected, what to do

C-Kermit before 11.1.515 contains a heap buffer overflow vulnerability in putsrv() in ckcfns.c that allows malicious peers to write past the srvcmd buffer by sending crafted packets. Attackers can use Kermit repeat-count compression in server command, GET, or file-header packets to write attacker-chosen bytes beyond the heap buffer on servers or receiving instances.

Update OpenKermit C-Kermit to version 11.1.515.

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

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Metrics

9.2

XIEM Effective CVSS

Highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v4

8.1

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: Critical
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: 76.00 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: 9.2 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: 8.1
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: 9.2
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-122

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	`< 11.1.515`	`11.1.515`

Vendors and products

Openkermit C-kermit

Weakness classes (CWE)

CWE-122Heap-based Buffer Overflow
Variant
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
Entry at MITRE CWE-122

References & sources

github.comGitHub Security Advisory (GHSA-c5px-7h4c-gj8p)euvd, Vendor advisory, advisory
github.comOpenKermit/ckermit/commit/37e54720779237897bc6887efac42fe138817…euvd, Patch
github.comC-Kermit v11.1.515 Release Noteseuvd, Release notes, advisory
github.comOpenKermit/ckermit/blob/v11.0.514/ckcfns.ceuvd, Technical description
vulncheck.comVulnCheck Advisory: C-Kermit before 11.1.515 Heap Buffer Overflow via putsrv() Packet Decodingeuvd, Third-party advisory
NVD (NIST)vuln/detail/CVE-2026-129126euvd
github.comCVEProject/cvelistV5/tree/main/cves/2026/129xxx/CVE-2026-129122…advisory
github.comOpenKermit/ckermit/blob/v11.0.514/ckctel.carticle
github.comOpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc…fix
github.comOpenKermit/ckermit/commit/42cf6decb926f56d606a76262791aaf071955…fix
NVD (NIST)vuln/detail/CVE-2026-129122advisory
vulncheck.comadvisories/c-kermit-6.0.192-before-11.1.515-buffer-overflow-via…advisory
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

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:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

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

Weakness type: CWE-122

Description added or changed

New references:

and 1 more reference

Show 10 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	C-Kermit before 11.1.515 contains a heap buffer overflow vulnerability in putsrv() in ckcfns.c that allows malicious peers to write past the srvcmd buffer by sending crafted packets. Attackers can use Kermit repeat-count compression in server command, GET, or file-header packets to write attacker-chosen bytes beyond the heap buffer on servers or receiving instances.
CVSS	added	—	AV:N/AC:L/AT:P/PR:N/UI:N/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:N/S:U/C:H/I:H/A:H
Weakness type (CWE)	added	—	CWE-122
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/129xxx/CVE-2026-129126.json">CVE-2026-129126</a>
Reference	added	—	https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckcfns.c#L461
Reference	added	—	https://github.com/OpenKermit/ckermit/commit/37e54720779237897bc6887efac42fe138817897
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-before-11.1.515-heap-buffer-overflow-via-putsrv-packet-decoding

Source identifier: disclosure@vulncheck.com

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