CVE-2023-27729: Nginx NJS v0.7.10 was discovered to contain an illegal memcpy via the function njs_vmcode_return at src/njs_vm

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HIGH 7.5REMOTEWATCHLISTDOWNGRADE

CVE-2023-27729 is a high-severity flaw (CVSS 7.5) affecting njs. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Nginx NJS v0.7.10 was discovered to contain an illegal memcpy via the function njs_vmcode_return at src/njs_vmcode.c.

Why this priority

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

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

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 49%)
CISA exploited list	No
Weakness	CWE-119
Published	2023-04-09
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: f5

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

Am I affected?

Timeline

2023-04-09 20:15 UTCPublished CVE record published
2026-06-17 05:45 UTCUpdated Record last modified

f5 njs DOWNGRADE

Affected: 0.7.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.7.10

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 0.7.10 (Debian / Ubuntu)

apt-cache madison njs sudo apt install njs=<VERSION_BEFORE_0.7.10> sudo apt-mark hold njs

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

dnf --showduplicates list njs sudo dnf downgrade njs-<VERSION_BEFORE_0.7.10> sudo dnf versionlock add njs

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-2023-27729?

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

Is CVE-2023-27729 being exploited?

CVE-2023-27729 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-2023-27729 affect?

CVE-2023-27729 affects njs. Severity is high (CVSS 7.5). Nginx NJS v0.7.10 was discovered to contain an illegal memcpy via the function njs_vmcode_return at src/njs_vmcode.c.

How urgent is CVE-2023-27729?

Priority 49/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

nginx vulnerabilities · F5 BIG-IP vulnerabilities

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References

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