CVE-2026-129122 is a high-severity (CVSS 7.5) Out-of-bounds Write vulnerability in OpenKermit C-Kermit. A fix is available — see the affected versions and patch details below.
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…
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
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Description
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.
Affected Products
C-KermitOpenKermitDetection & mitigation playbook
Vendor / applianceDetect
Inventory every OpenKermit C-Kermit deployment and check each version against the affected-products list above.
Fix
Apply the OpenKermit C-Kermit security patch or hotfix for CVE-2026-129122 on the affected version, following the vendor advisory for your exact build.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
Frequently Asked Questions
Is CVE-2026-129122 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.