CVE-2023-24609: Matrix SSL 4.x through 4.6.0 and Rambus TLS Toolkit have a length-subtraction integer overflow for Client Hell

This week

HIGH 7.5REMOTEUPGRADEMITIGATE

CVE-2023-24609 is a high-severity flaw (CVSS 7.5) affecting matrixssl, tls toolkit. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Matrix SSL 4.x through 4.6.0 and Rambus TLS Toolkit have a length-subtraction integer overflow for Client Hello Pre-Shared Key extension parsing in the TLS 1.3 server. An attacked device calculates an SHA-2 hash over at least 65 KB (in RAM). With a large number of crafted TLS messages, the CPU becomes heavily loaded. This occurs in tls13VerifyBinder and tls13TranscriptHashUpdate.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-190
Published	2023-12-22
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: matrixssl · rambus

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2023-12-22 04:15 UTCPublished CVE record published
2026-06-17 05:39 UTCUpdated Record last modified

matrixssl matrixssl UPGRADE

Affected: >= 4.0.0 and <= 4.6.0

Fixed in: newer than 4.6.0

Safe to downgrade to: a release before 4.0.0

1. Check installed version

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

2. UPGRADE to newer than 4.6.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade matrixssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade matrixssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.0.0 (Debian / Ubuntu)

apt-cache madison matrixssl sudo apt install matrixssl=<VERSION_BEFORE_4.0.0> sudo apt-mark hold matrixssl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list matrixssl sudo dnf downgrade matrixssl-<VERSION_BEFORE_4.0.0> sudo dnf versionlock add matrixssl

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.

rambus tls toolkit MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy tls-toolkit || rpm -q tls-toolkit || tls-toolkit --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

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-2023-24609?

matrixssl: upgrade to newer than 4.6.0; tls toolkit: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2023-24609 being exploited?

CVE-2023-24609 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-2023-24609 affect?

CVE-2023-24609 affects matrixssl, tls toolkit. Severity is high (CVSS 7.5). Matrix SSL 4.x through 4.6.0 and Rambus TLS Toolkit have a length-subtraction integer overflow for Client Hello Pre-Shared Key extension parsing in the TLS 1.3 server. An attacked device calculates an SHA-2 hash over at least 65 KB (in RAM)

How urgent is CVE-2023-24609?

Priority 50/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2022-46505 HIGH 7.5 UPGRADE An issue in MatrixSSL 4.5.1-open and earlier leads to failure to securely check the SessionID field, resulting
CVE-2022-43974 HIGH 8.1 UPGRADE MatrixSSL 4.0.4 through 4.5.1 has an integer overflow in matrixSslDecodeTls13

References

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