How severe is CVE-2026-33805?

CVE-2026-33805 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-33805 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33805?

CVE-2026-33805 primarily affects Fastify Fastify/http-proxy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-33805?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-33805 have an EU (EUVD) identifier?

Yes. CVE-2026-33805 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-22877.

When was CVE-2026-33805 published?

CVE-2026-33805 was published on 2026-04-15 and last updated on 2026-06-30.

CVE-2026-33805

CVE-2026-33805 is a high-severity vulnerability in Fastify Fastify/http-proxy with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-644.

Key facts

Severity: High (CVSS 3.x base score 8.6)
CVSS v4: 9.0
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-22877
Weakness: CWE-644
Affected product: Fastify Fastify/http-proxy
Published: 2026-04-15
Last modified: 2026-06-30

Description

@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from. Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.

Frequently asked questions

What is CVE-2026-33805?: @fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from. Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.
How severe is CVE-2026-33805?: CVE-2026-33805 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-33805 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33805?: CVE-2026-33805 primarily affects Fastify Fastify/http-proxy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-33805?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-33805 have an EU (EUVD) identifier?: Yes. CVE-2026-33805 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-22877.
When was CVE-2026-33805 published?: CVE-2026-33805 was published on 2026-04-15 and last updated on 2026-06-30.

References

Affected products (2)

cpe:2.3:a:fastify:fastify\/http-proxy:*:*:*:*:*:node.js:*:*
cpe:2.3:a:fastify:reply-from:*:*:*:*:*:node.js:*:*

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