CVE-2026-5590: A race condition during TCP connection teardown can cause tcp_recv() to operate on a connection that has alrea

Q: How do I fix CVE-2026-5590?

zephyr: upgrade to newer than 4.3.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-5590 being exploited?

CVE-2026-5590 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-2026-5590 affect?

CVE-2026-5590 affects zephyr. Severity is medium (CVSS 6.4). A race condition during TCP connection teardown can cause tcp_recv() to operate on a connection that has already been released. If tcp_conn_search() returns NULL while processing a SYN packet, a NULL pointer derived from stale context data

Q: How urgent is CVE-2026-5590?

Priority 30/100. Public exploit reference

Routine

MEDIUM 6.4UPGRADE

CVE-2026-5590 is a medium-severity flaw (CVSS 6.4) affecting zephyr. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A race condition during TCP connection teardown can cause tcp_recv() to operate on a connection that has already been released. If tcp_conn_search() returns NULL while processing a SYN packet, a NULL pointer derived from stale context data is passed to tcp_backlog_is_full() and dereferenced without validation, leading to a crash.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	6.4 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 90%)
CISA exploited list	No
Weakness	CWE-476
Published	2026-04-05
Last modified	2026-10-15

Publisher (CNA): Zephyr Project · Vendor: zephyrproject

Last updated 2026-10-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-05 04:16 UTCPublished CVE record published
2026-10-15 23:17 UTCUpdated Record last modified

zephyrproject zephyr UPGRADE

Affected: <= 4.3.0

Fixed in: newer than 4.3.0

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2026-5590?

zephyr: upgrade to newer than 4.3.0. Exact commands for each OS are on this page.

Is CVE-2026-5590 being exploited?

CVE-2026-5590 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-2026-5590 affect?

CVE-2026-5590 affects zephyr. Severity is medium (CVSS 6.4). A race condition during TCP connection teardown can cause tcp_recv() to operate on a connection that has already been released. If tcp_conn_search() returns NULL while processing a SYN packet, a NULL pointer derived from stale context data

How urgent is CVE-2026-5590?

Priority 30/100. Public exploit reference

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References

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