CVE-2026-84783: Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached

Q: How do I fix CVE-2026-84783?

openssl: upgrade to 4.0.3. Exact commands for each OS are on this page.

Q: Is CVE-2026-84783 being exploited?

CVE-2026-84783 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-84783 affect?

CVE-2026-84783 affects openssl. Severity is high (CVSS 7.5). Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached extension data to be freed while another thread is still using it. Impact summary: A remote, unauthenticated peer could crash a m

Q: How urgent is CVE-2026-84783?

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

This month

HIGH 7.5REMOTEWATCHLISTUPGRADE

CVE-2026-84783 is a high-severity flaw (CVSS 7.5) affecting openssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached extension data to be freed while another thread is still using it. Impact summary: A remote, unauthenticated peer could crash a multi-threaded TLS client, or a multi-threaded TLS server that requests client certificates, if the first certificate chains built to the same trusted CA certificate are built by several connections at the same

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

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	0.3% (top 79%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-09-29
Last modified	2026-10-08

Publisher (CNA): OpenSSL Software Foundation · Vendor: openssl

Last updated 2026-10-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-29 16:17 UTCPublished CVE record published
2026-10-08 01:21 UTCUpdated Record last modified

openssl openssl UPGRADE

Affected: >= 4.0.0 and < 4.0.3

Fixed in: 4.0.3

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 4.0.3 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade openssl

Note

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

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-2026-84783?

openssl: upgrade to 4.0.3. Exact commands for each OS are on this page.

Is CVE-2026-84783 being exploited?

CVE-2026-84783 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-2026-84783 affect?

CVE-2026-84783 affects openssl. Severity is high (CVSS 7.5). Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached extension data to be freed while another thread is still using it. Impact summary: A remote, unauthenticated peer could crash a m

How urgent is CVE-2026-84783?

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

Software pages

OpenSSL vulnerabilities

Related CVEs

CVE-2026-84784 HIGH 7.5 UPGRADE Issue summary: A malicious remote peer may flood the local QUIC stack with NEW_CONNECTION_ID frames by avoidin
CVE-2026-84782 HIGH 8.2 UPGRADE Issue summary: The DTLS retransmission logic does not correctly handle a handshake message write that is suspe
CVE-2026-77696 LOW 3.7 UPGRADE Issue summary: SM2 signature generation uses non-constant-time arithmetic on secret values, forming a timing s
CVE-2026-75806 MEDIUM 5.3 UPGRADE Issue summary: An established DTLS 1.2 association using an AEAD cipher suite can be terminated by a single un
CVE-2026-75805 MEDIUM 5.3 UPGRADE Issue summary: A CMP client that requests certificate revocation on the basis of a PKCS#10 CSR may dereference

References

← Back to latest CVEs