Vulnerability · Published Nov 4, 2026 · Assigned by VulnCheck

CVE-2026-122127CESNET ipfixcol2 2.7.1 before 2.9.0 Heap Buffer Overflow via TCP LZ4 Decoder

High 7.5

In plain English

A high-severity out-of-bounds write in ipfixcol2 from CESNET. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 33% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.4%top 67.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

CESNET ipfixcol2 2.7.1 before 2.9.0 contains a heap-based buffer overflow in Lz4Decoder.cpp that allows unauthenticated network peers to write past heap buffers. Attackers can declare a small ring buffer_size followed by a large decompressed_size to write up to 65535 controlled bytes and crash the collector.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	ipfixcol2	2.9.0-1	DEBIAN-CVE-2026-122127
Ubuntu:26.10	ipfixcol2	no fix listed	UBUNTU-CVE-2026-122127

Affected products (as reported)

Vendor	Product	Versions
CESNET	ipfixcol2	2.7.1 – before 2.9.0

Weakness: CWE-787 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

Patch Commit patch
https://github.com/CESNET/ipfixcol2 product
ipfixcol2 v2.9.0 Release Notes release-notes
https://github.com/CESNET/ipfixcol2/blob/v2.8.0/src/plugins/input/tcp/src/Lz4Decoder.cpp#L139-L151 technical-description
VulnCheck Advisory: CESNET ipfixcol2 2.7.1 before 2.9.0 Heap Buffer Overflow via TCP LZ4 Decoder third-party-advisory