VDB-357705 · CVE-2026-33805 · GCVE-0-2026-33805

fastify reply-from/http-proxy prior 12.6.2 Header rewriteRequestHeaders Connection http headers for scripting syntax

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
7.0	$0-$5k	0.00

Summaryinfo

A vulnerability was found in fastify reply-from and http-proxy. It has been classified as critical. The impacted element is the function rewriteRequestHeaders of the component Header Handler. Performing a manipulation of the argument Connection results in improper neutralization of http headers for scripting syntax. This vulnerability is known as CVE-2026-33805. Remote exploitation of the attack is possible. No exploit is available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in fastify reply-from and http-proxy. This affects the function rewriteRequestHeaders of the component Header Handler. The manipulation of the argument Connection with an unknown input leads to a improper neutralization of http headers for scripting syntax vulnerability. CWE is classifying the issue as CWE-644. The product does not neutralize or incorrectly neutralizes web scripting syntax in HTTP headers that can be used by web browser components that can process raw headers, such as Flash. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

@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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-33805 since 03/23/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available.

Upgrading to version 12.6.2 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

Firewall Software

Vendor

fastify

Name

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 7.3
VulDB Meta Temp Score: 7.0

VulDB Base Score: 7.3
VulDB Temp Score: 7.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AV	AC	Au	C	I	A
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💳	💳	💳	💳	💳	💳
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Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Improper neutralization of http headers for scripting syntax
CWE: CWE-644
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: reply-from/http-proxy 12.6.2

Timelineinfo

03/23/2026 CVE reserved
04/15/2026 +22 days Advisory disclosed
04/15/2026 +0 days VulDB entry created
04/15/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-33805 (🔒)
GCVE (CVE): GCVE-0-2026-33805
GCVE (VulDB): GCVE-100-357705

Entryinfo

Created: 04/15/2026 13:59
Changes: 04/15/2026 13:59 (68)
Complete: 🔍
Cache ID: 216::103