# CVE-2026-129123: C-Kermit 8.0.200 before 11.1.515 FTP Client Buffer Overflow via PBSZ and ADAT Replies

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

C-Kermit 8.0.200 before 11.1.515 contains a buffer overflow vulnerability in getreply() in ckcftp.c that allows malicious FTP servers to overwrite client memory by sending overlong security replies. Attackers controlling or intercepting an FTP server can send long PBSZ replies after AUTH TLS, or long ADAT replies in GSSAPI, Kerberos 4, and SRP builds, overflowing the static reply_buf with attacker-controlled bytes.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/OpenKermit/ckermit/commit/bec28a4d544031fa07a07aacba3df5dd1202ef69

## Affected products and versions

- OpenKermit / C-Kermit (OpenKermit/ckermit): ≥ 8.0.200; < 11.1.515 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: CNA: VulnCheck

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/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; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: exploitation poc; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-120

## Exploit evidence

- exploit: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p (ADP: CISA-ADP)

## References

- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p (CNA: VulnCheck; vendor-advisory)

- https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f (CNA: VulnCheck; patch)

- https://github.com/OpenKermit/ckermit/commit/bec28a4d544031fa07a07aacba3df5dd1202ef69 (CNA: VulnCheck; patch)

- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515 (CNA: VulnCheck; release-notes)

- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckcftp.c#L11161 (CNA: VulnCheck; technical-description)

- https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-ftp-client-buffer-overflow-via-pbsz-and-adat-replies (CNA: VulnCheck; third-party-advisory)

- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p (ADP: CISA-ADP; exploit)

- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckcftp.c#L11161 (disclosure@vulncheck.com)

- https://github.com/OpenKermit/ckermit/commit/39ab009a365b97632e9975e1266fa618c4bdc59f (disclosure@vulncheck.com)

- https://github.com/OpenKermit/ckermit/commit/bec28a4d544031fa07a07aacba3df5dd1202ef69 (disclosure@vulncheck.com)

- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515 (disclosure@vulncheck.com)

- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/c-kermit-8.0.200-before-11.1.515-ftp-client-buffer-overflow-via-pbsz-and-adat-replies (disclosure@vulncheck.com)

- https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p (134c704f-9b21-4f2e-91b3-4a467353bcc0)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-129123; retrieved 2026-11-13; source updated 2026-11-13

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-129123; retrieved 2026-11-14; source updated 2026-11-13

Revision: 920f6b16794c30b97b48397815143a8ddcd7d692a096295980fa58f005f928c8

Canonical: https://y2.dev/cve/CVE-2026-129123

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