CVE-2026-33806: Impact: Fastify applications using schema.body.content for per-content-type body validation can have validati

Q: How do I fix CVE-2026-33806?

fastify: upgrade to 5.8.5. Exact commands for each OS are on this page.

Q: Is CVE-2026-33806 being exploited?

CVE-2026-33806 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-2026-33806 affect?

CVE-2026-33806 affects fastify. Severity is high (CVSS 7.5). Impact: Fastify applications using schema.body.content for per-content-type body validation can have validation bypassed entirely by prepending a space to the Content-Type header. The body is still parsed correctly but schema validation is

Q: How urgent is CVE-2026-33806?

Priority 41/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-33806 is a high-severity flaw (CVSS 7.5) affecting fastify. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Impact: Fastify applications using schema.body.content for per-content-type body validation can have validation bypassed entirely by prepending a space to the Content-Type header. The body is still parsed correctly but schema validation is skipped. This is a regression introduced in fastify >= 5.3.2 by the fix for CVE-2025-32442 Patches: Upgrade to fastify v5.8.5 or later. Workarounds: None. Upgrade to the patched version.

Why this priority

High severity
Remotely exploitable, no login, no user action

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	0.4% (top 61%)
CISA exploited list	No
Weakness	CWE-1287, CWE-1289
Published	2026-04-15
Last modified	2026-07-15

Publisher (CNA): openjs · Vendor: fastify

Last updated 2026-07-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-15 04:17 UTCPublished CVE record published
2026-07-15 02:20 UTCUpdated Record last modified

fastify fastify UPGRADE

Affected: >= 5.3.2 and < 5.8.5

Fixed in: 5.8.5

Safe to downgrade to: a release before 5.3.2

1. Check installed version

npm ls fastify

2. UPGRADE to 5.8.5

npm install fastify@">=5.8.5"

3. If no update is available yet, DOWNGRADE to a release before 5.3.2

npm view fastify versions npm install fastify@"<5.3.2"

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-2026-33806?

fastify: upgrade to 5.8.5. Exact commands for each OS are on this page.

Is CVE-2026-33806 being exploited?

CVE-2026-33806 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-2026-33806 affect?

CVE-2026-33806 affects fastify. Severity is high (CVSS 7.5). Impact: Fastify applications using schema.body.content for per-content-type body validation can have validation bypassed entirely by prepending a space to the Content-Type header. The body is still parsed correctly but schema validation is

How urgent is CVE-2026-33806?

Priority 41/100. High severity; Remotely exploitable, no login, no user action

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References

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