CVE-2026-33806

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

Upgrade fastify to 5.8.5 or later.

Q: Is CVE-2026-33806 being actively exploited?

Not that we know of. CVE-2026-33806 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.45% is the estimated probability that it will be exploited in the next 30 days. That is higher than 37% of all scored CVEs.

Q: How severe is CVE-2026-33806?

CVE-2026-33806 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2026-33806 affect?

Published advisories record a fix for fastify (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

HIGH

7.5

CVSS v3

NVD

Description

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.

CWE-1287Improper Validation of Specified Type of Input CWE-1289

How to fix

Remediation Available

fastifyNVD

Affected:>= 5.3.2, < 5.8.5Fixed in:5.8.5CVE-2026-33806derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Exploit Intelligence

0.45%probability of exploitation in 30 days

37thpercentile

Low risk: more likely to be exploited than 37% of all known CVEs.

References

Vendor Advisory1

cna.openjsf.org

Other references4

Related Vulnerabilities

Other CWE-1287 (Improper Validation of Specified Type of Input) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-4879	Critical	9.8	100%	KEV	-
CVE-2022-31007	Medium	4.9	27%	-	Fix
CVE-2024-6298	Critical	10.0	19%	-	-
CVE-2026-25639	High	7.5	2.8%	-	Fix
CVE-2021-43802	Critical	9.9	2.0%	-	Fix
CVE-2026-5946	High	7.5	1.9%	-	Fix

Common questions

How do I fix CVE-2026-33806?

Upgrade fastify to 5.8.5 or later.

Is CVE-2026-33806 being actively exploited?

Not that we know of. CVE-2026-33806 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.45% is the estimated probability that it will be exploited in the next 30 days. That is higher than 37% of all scored CVEs.

How severe is CVE-2026-33806?

CVE-2026-33806 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-33806 affect?

Published advisories record a fix for fastify (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2026-33806

Markdown

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-15.