CVE-2006-3121: The peel_netstring function in cl_netstring.c in the heartbeat subsystem in High-Availability Linux before 1.2

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MEDIUM 5.0WATCHLISTDOWNGRADE

CVE-2006-3121 is a medium-severity flaw (CVSS 5.0) affecting heartbeat. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The peel_netstring function in cl_netstring.c in the heartbeat subsystem in High-Availability Linux before 1.2.5, and 2.0 before 2.0.7, allows remote attackers to cause a denial of service (crash) via the length parameter in a heartbeat message.

Why this priority

EPSS top 4%: very likely to be exploited
Public exploit reference
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.0 (Medium)
EPSS exploit chance	13.6% (top 4%)
CISA exploited list	No
Weakness	CWE-399
Published	2006-08-17
Last modified	2026-06-16

Publisher (CNA): Debian GNU/Linux · Vendor: high availability linux project

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2006-08-17 01:04 UTCPublished CVE record published
2026-06-16 22:26 UTCUpdated Record last modified

high availability linux project heartbeat DOWNGRADE

Affected: 1.2.3 · 1.2.4 · 2.0.1 · 2.0.2 · 2.0.3 · 2.0.4 · 2.0.5 · 2.0.6

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.2.3

1. Check installed version

apt-cache policy heartbeat || rpm -q heartbeat || heartbeat --version

2. No fixed release: DOWNGRADE to a release before 1.2.3 (Debian / Ubuntu)

apt-cache madison heartbeat sudo apt install heartbeat=<VERSION_BEFORE_1.2.3> sudo apt-mark hold heartbeat

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list heartbeat sudo dnf downgrade heartbeat-<VERSION_BEFORE_1.2.3> sudo dnf versionlock add heartbeat

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: Linux-HA Heartbeat 2.0.6 - Remote Denial of Service

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2006-3121?

heartbeat: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2006-3121 being exploited?

CVE-2006-3121 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2006-3121 affect?

CVE-2006-3121 affects heartbeat. Severity is medium (CVSS 5.0). The peel_netstring function in cl_netstring.c in the heartbeat subsystem in High-Availability Linux before 1.2.5, and 2.0 before 2.0.7, allows remote attackers to cause a denial of service (crash) via the length parameter in a heartbeat mes

How urgent is CVE-2006-3121?

Priority 52/100. EPSS top 4%: very likely to be exploited; Public exploit reference; On your watchlist

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References

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