CVE
C-Kermit remote heap buffer overflow in packet decoding
- Exploited
- No known exploitation
- Fix
- Fixed in 11.1.515
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 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? →
- 26/100 · 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? →
- Unclear
- 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 from OpenKermit, before version 11.1.515, has a heap buffer overflow in its packet decoding that lets an attacker write attacker-chosen bytes past a heap buffer. A remote attacker can trigger it without logging in by sending crafted Kermit packets to a server or receiving instance.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
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.
Who should check
Teams running C-Kermit before 11.1.515 as a server or as a file receiver fed by peers
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity9.2/10CVSS 9.2
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
- Would score about 31 if advisories confirm default setups are exposed
What to do
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-2026-129126 (C-Kermit before 11.1.515 Heap Buffer Overflow via putsrv() Packet Decoding), 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-2026-129126 (entry last updated 2026-11-13):
Affected:
- OpenKermit C-Kermit: fixed in 11.1.515
Fixed versions: 11.1.515.
Conditions (all must be true for the bug to be hit):
- C-Kermit running in server mode (not IKSD) (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p)
- C-Kermit receiving files from a peer (source: https://github.com/OpenKermit/ckermit/security/advisories/GHSA-c5px-7h4c-gj8p)
- C-Kermit versions before 11.1.515 (source: https://www.vulncheck.com/advisories/c-kermit-before-11.1.515-heap-buffer-overflow-via-putsrv-packet-decoding)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-129126 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-129126 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/37e54720779237897bc6887efac42fe138817897
- https://github.com/OpenKermit/ckermit/releases/tag/v11.1.515
- https://github.com/OpenKermit/ckermit/blob/v11.0.514/ckcfns.c#L461
- https://www.vulncheck.com/advisories/c-kermit-before-11.1.515-heap-buffer-overflow-via-putsrv-packet-decoding
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-2026-129126
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-2026-129126"}.Timeline
- CVE published
- First seen by cve.now
- Posted on X by cve.now
Affected versions
- OpenKermit C-Kermit
fixed in 11.1.515
Evidence 6
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-129126
Is CVE-2026-129126 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?
A malicious peer can write attacker-chosen bytes past a heap buffer in C-Kermit, corrupting heap memory. The flaw is in how C-Kermit decodes packets in putsrv().Source: github.com, vulncheck.com
Which versions are affected by CVE-2026-129126?
C-Kermit: before 11.1.515.Source: cve.now feed data
Am I affected, and how do I check?
C-Kermit versions before 11.1.515 are affected, when running in server mode (not IKSD) or when receiving files from a peer. To check, run the C-Kermit version command and compare the version with 11.1.515.Source: github.com, vulncheck.com
How do I fix CVE-2026-129126?
Upgrade C-Kermit to version 11.1.515 or later, which is the fixed version.Source: github.com, vulncheck.com