CVE-2026-16158: Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache ke

Q: How do I fix CVE-2026-16158?

fastify\/reply-from: upgrade to 12.6.4. Exact commands for each OS are on this page.

Q: Is CVE-2026-16158 being exploited?

CVE-2026-16158 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-2026-16158 affect?

CVE-2026-16158 affects fastify\/reply-from. Severity is high (CVSS 8.7). Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different destination and source pairs can therefore produ

Q: How urgent is CVE-2026-16158?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 8.7REMOTEUPGRADE

CVE-2026-16158 is a high-severity flaw (CVSS 8.7) affecting fastify\/reply-from. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different destination and source pairs can therefore produce the same key while resolving to different upstream URLs. When getUpstream selects an upstream from request data, a URL cached for one upstream can be reused for a request intended for another upstream, causi

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.7 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 68%)
CISA exploited list	No
Weakness	CWE-441
Published	2026-07-18
Last modified	2026-08-05

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-08-05 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-18 13:17 UTCPublished CVE record published
2026-08-05 19:46 UTCUpdated Record last modified

fastify fastify\/reply-from UPGRADE

Affected: >= 8.3.1 and < 12.6.4

Fixed in: 12.6.4

Safe to downgrade to: a release before 8.3.1

1. Check installed version

npm ls fastifyreply-from

2. UPGRADE to 12.6.4

npm install fastifyreply-from@">=12.6.4"

3. If no update is available yet, DOWNGRADE to a release before 8.3.1

npm view fastifyreply-from versions npm install fastifyreply-from@"<8.3.1"

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-2026-16158?

fastify\/reply-from: upgrade to 12.6.4. Exact commands for each OS are on this page.

Is CVE-2026-16158 being exploited?

CVE-2026-16158 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-2026-16158 affect?

CVE-2026-16158 affects fastify\/reply-from. Severity is high (CVSS 8.7). Impact: @fastify/reply-from versions from 8.3.1 up to but not including 12.6.4 build the internal URL cache key by concatenating the destination and source path without a delimiter. Different destination and source pairs can therefore produ

How urgent is CVE-2026-16158?

Priority 43/100. High severity; Remotely exploitable, no login, no user action

References

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