CVE-2026-6679: A heap buffer overflow could occur in the DTLS 1.3 ACK serialization path before the connecting peer is authen

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-6679 is a high-severity flaw (CVSS 7.5) affecting wolfssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A heap buffer overflow could occur in the DTLS 1.3 ACK serialization path before the connecting peer is authenticated. The buffer overflow was due to an integer truncation when computing the length of the ACK record-number list, causing an undersized buffer to be allocated and then overrun. This affects builds using DTLS 1.3 and wolfSSL version 5.9.0 and earlier. A fix was added to the 5.9.1 release.

Why this priority

High severity
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	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-190, CWE-197, CWE-787
Published	2026-06-25
Last modified	2026-06-27

Publisher (CNA): wolfSSL Inc. · Vendor: wolfssl

Last updated 2026-06-27 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-25 21:16 UTCPublished CVE record published
2026-06-27 20:26 UTCUpdated Record last modified

wolfssl wolfssl UPGRADE

Affected: >= 5.4.0 and < 5.9.1

Fixed in: 5.9.1

Safe to downgrade to: a release before 5.4.0

1. Check installed version

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

2. UPGRADE to 5.9.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade wolfssl

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 5.4.0 (Debian / Ubuntu)

apt-cache madison wolfssl sudo apt install wolfssl=<VERSION_BEFORE_5.4.0> sudo apt-mark hold wolfssl

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

dnf --showduplicates list wolfssl sudo dnf downgrade wolfssl-<VERSION_BEFORE_5.4.0> sudo dnf versionlock add wolfssl

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.

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-2026-6679?

wolfssl: upgrade to 5.9.1. Exact commands for each OS are on this page.

Is CVE-2026-6679 being exploited?

CVE-2026-6679 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-2026-6679 affect?

CVE-2026-6679 affects wolfssl. Severity is high (CVSS 7.5). A heap buffer overflow could occur in the DTLS 1.3 ACK serialization path before the connecting peer is authenticated. The buffer overflow was due to an integer truncation when computing the length of the ACK record-number list, causing an

How urgent is CVE-2026-6679?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

Software pages

wolfSSL vulnerabilities

Related CVEs

CVE-2026-55967 HIGH 7.5 UPGRADE AES-GCM encryption/decryption with extremely large cumulative single message sizes (>64 GiB) were not properly
CVE-2026-7532 HIGH 7.5 UPGRADE iPAddress name constraints bypass when WOLFSSL_IP_ALT_NAME is not defined
CVE-2026-6678 MEDIUM 5.3 UPGRADE Integer underflow in wc_PKCS7_DecryptOri when handling crafted Other Recipient Info, leading to incorrect leng
CVE-2026-6681 MEDIUM 5.3 UPGRADE The PKCS#7 decode path ignores the caller-supplied output buffer size (outputSz), allowing decoded content to
CVE-2026-6731 HIGH 7.5 UPGRADE X.509 name constraint bypass via the Subject Common Name when treated as a DNS-type name

References

← Back to latest CVEs