Is CVE-2026-33808 in the CISA KEV catalog?

No. CVE-2026-33808 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-33808?

CVE-2026-33808 has a CVSS v3 base score of 9.1 (CRITICAL).

What is the EPSS score for CVE-2026-33808?

CVE-2026-33808 has an EPSS score of 0.48% (39th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-33808?

Upgrade fastify\/express to 4.0.5 or later.

CVE & CISA-KEV Catalog

CVE-2026-33808

CRITICAL

9.1

CVSS v3

NVD

Description

Impact@fastify/express v4.0.4 and earlier fails to normalize URLs before passing them to Express middleware when Fastify router normalization options are enabled. This allows complete bypass of path-scoped authentication middleware via duplicate slashes when ignoreDuplicateSlashes is enabled, or via semicolon delimiters when useSemicolonDelimiter is enabled. In both cases, Fastify router normalizes the URL and matches the route, but @fastify/express passes the original un-normalized URL to Express middleware, which fails to match and is skipped. An unauthenticated attacker can access protected routes by manipulating the URL path. PatchesUpgrade to @fastify/express v4.0.5 or later.

CWE-436

How to fix

Remediation Available

fastify\/expressNVD

Affected:< 4.0.5Fixed in:4.0.5CVE-2026-33808derived 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

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

0.48%probability of exploitation in 30 days

39thpercentile

Low risk: more likely to be exploited than 39% of all known CVEs.

References

Exploit1

github.com

Vendor Advisory1

cna.openjsf.org

Related Vulnerabilities

Other CWE-436 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-25292	Critical	9.8	64%	-	Fix
CVE-2022-37436	Medium	5.3	58%	-	Fix
CVE-2021-28474	High	8.8	51%	-	Fix
CVE-2025-25291	Critical	9.8	20%	-	Fix
CVE-2026-63030	Critical	9.8	8.9%	KEV	Fix
CVE-2019-17596	High	7.5	4.7%	-	Fix

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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 2026-06-01.