CVE-2026-18540: undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an e

Q: How do I fix CVE-2026-18540?

undici: upgrade to 6.28.1, 7.29.1, 8.10.2. Exact commands for each OS are on this page.

Q: Is CVE-2026-18540 being exploited?

CVE-2026-18540 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-2026-18540 affect?

CVE-2026-18540 affects undici. Severity is low (CVSS 3.7). undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server de

Q: How urgent is CVE-2026-18540?

Priority 24/100. Remotely exploitable, no login, no user action

Routine

LOW 3.7REMOTEUPGRADE

CVE-2026-18540 is a low-severity flaw (CVSS 3.7) affecting undici. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server delivers part of a body without a trustworthy resume checkpoint, for example a non-success response whose headers were already sent or a partial-content response with an unusable content range, then closes the co

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	3.7 (Low)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 76%)
CISA exploited list	No
Weakness	CWE-444
Published	2026-09-04
Last modified	2026-09-16

Publisher (CNA): openjs · Vendor: nodejs

Last updated 2026-09-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-04 18:17 UTCPublished CVE record published
2026-09-16 20:41 UTCUpdated Record last modified

nodejs undici UPGRADE

Affected: < 6.28.1 · >= 7.0.0 and < 7.29.1 · >= 8.0.0 and < 8.10.2

Fixed in: 6.28.1, 7.29.1, 8.10.2

Safe to downgrade to: a release before 7.0.0

1. Check installed version

npm ls undici

2. UPGRADE to 6.28.1

npm install undici@">=6.28.1"

3. If no update is available yet, DOWNGRADE to a release before 7.0.0

npm view undici versions npm install undici@"<7.0.0"

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.

Advisories and coverage

Official advisories

Amazon Linux 2023 ALAS: ALAS2023-2026-3277 (important): nodejs22 2026-10-24

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-2026-18540?

undici: upgrade to 6.28.1, 7.29.1, 8.10.2. Exact commands for each OS are on this page.

Is CVE-2026-18540 being exploited?

CVE-2026-18540 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-2026-18540 affect?

CVE-2026-18540 affects undici. Severity is low (CVSS 3.7). undici's retry interceptor can append the body of a ranged retry response to bytes already delivered from an earlier partial response while still presenting the original response's status and headers. This happens when an upstream server de

How urgent is CVE-2026-18540?

Priority 24/100. Remotely exploitable, no login, no user action

Software pages

Node.js vulnerabilities · Check Point vulnerabilities

Related CVEs

CVE-2026-109855 HIGH 7.5 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109383 HIGH 7.4 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109829 HIGH 7.4 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109841 MEDIUM 5.9 UPGRADE undici is an HTTP client library for Node.js
CVE-2026-109869 HIGH 7.5 UPGRADE undici is an HTTP client library for Node.js

References

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