CVE
C-Kermit buffer overflow in Telnet NEW-ENVIRON handling
- Exploited
- No known exploitation
- Fix
- Fixed in 11.1.515
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. C-Kermit is used as a Telnet client and connects to a malicious or man-in-the-middle server. Affected versions are C-Kermit 6.0.192 up to but not including 11.1.515.
- Published
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 20/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
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.
Who should check
Teams running C-Kermit 6.0.192 through 11.1.514 as a Telnet client that connects to servers they do not fully trust, including man-in-the-middle paths.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure12/25Specific setups only, reachable over the network without a login
- Reach?/20Unknown. No tracked technology or package matched
- Severity7.7/10CVSS 7.7
- No patch0/5No signal
What would change the score
- Would score about 70 if added to CISA KEV
- Would score about 65 if CISA's SSVC rates exploitation active
What to do
Check whether your setup matches what the bug needs.
C-Kermit is used as a Telnet client and connects to a malicious or man-in-the-middle server. Affected versions are C-Kermit 6.0.192 up to but not including 11.1.515.Upgrade to a fixed version: 11.1.515.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-129122 (C-Kermit 6.0.192 before 11.1.515 Buffer Overflow via Telnet NEW-ENVIRON Negotiation), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-129122 (entry last updated 2026-11-13):
Affected:
- OpenKermit C-Kermit: from 6.0.192, fixed in 11.1.515
Fixed versions: 11.1.515.
Conditions (all must be true for the bug to be hit):
- C-Kermit is used as a Telnet client and connects to a malicious or man-in-the-middle server. (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p)
- Affected versions are C-Kermit 6.0.192 up to but not including 11.1.515. (source: https://www.vulncheck.com/advisories/c-kermit-6.0.192-before-11.1.515-buffer-overflow-via-telnet-new-environ-negotiation)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, a user action.
CISA KEV: CVE-2026-129122 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-129122 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p
- https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f
- https://github.com/OpenKermit/ckermit/commit/42cf6decb926f56d606a76262791aaf071955d25
- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckctel.c#L5622
- https://www.vulncheck.com/advisories/c-kermit-6.0.192-before-11.1.515-buffer-overflow-via-telnet-new-environ-negotiation
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-129122
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-129122"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- OpenKermit C-Kermit
From 6.0.192 · fixed in 11.1.515
Evidence 7
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
Other links · 5
- Patch
- Patch
- Repository
- Repository
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-129122
Is CVE-2026-129122 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
When C-Kermit acts as a Telnet client, it mishandles NEW-ENVIRON SEND data sent by the server. Oversized variable names overflow a 16-byte stack buffer and a miscomputed heap buffer, corrupting stack and heap memory.Source: github.com, vulncheck.com
Which versions are affected by CVE-2026-129122?
C-Kermit: from 6.0.192 before 11.1.515.Source: cve.now feed data
Am I affected, and how do I check?
C-Kermit 6.0.192 up to but not including 11.1.515 is affected, and only when it is used as a Telnet client connecting to a malicious or man-in-the-middle server. Check the installed version with the C-Kermit version command and whether Telnet connections are used.Source: github.com, vulncheck.com
How do I fix CVE-2026-129122?
Upgrade C-Kermit to 11.1.515 or later, which is the fixed version.Source: github.com, vulncheck.com