CVE-2026-3635 | Fastify up to 5.8.2 request.protocol/request.host X-Forwarded-Proto/X-Forwarded-Host less trusted source (GHSA-444r-cwp2-x5xf)

VDB-352519 · CVE-2026-3635 · GHSA-444R-CWP2-X5XF FASTIFY UP TO 5.8.2 REQUEST.PROTOCOL/REQUEST.HOST X-FORWARDED-PROTO/X-FORWARDED-HOST LESS TRUSTED SOURCE HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 4.5 $0-$5k 2.89+ Summaryinfo A vulnerability classified as problematic has been found in Fastify up to 5.8.2. This affects the function request.protocol/request.host. This manipulation of the argument X-Forwarded-Proto/X-Forwarded-Host causes less trusted source. The identification of this vulnerability is CVE-2026-3635. The attack needs to be done within the local network. There is no exploit available. It is recommended to upgrade the affected component. Detailsinfo A vulnerability was found in Fastify up to 5.8.2. It has been declared as problematic. Affected by this vulnerability is the function request.protocol/request.host. The manipulation of the argument X-Forwarded-Proto/X-Forwarded-Host with an unknown input leads to a less trusted source vulnerability. The CWE definition for the vulnerability is CWE-348. The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack. As an impact it is known to affect confidentiality. The summary by CVE is: Summary When trustProxy is configured with a restrictive trust function (e.g., a specific IP like trustProxy: '10.0.0.1', a subnet, a hop count, or a custom function), the request.protocol and request.host getters read X-Forwarded-Proto and X-Forwarded-Host headers from any connection — including connections from untrusted IPs. This allows an attacker connecting directly to Fastify (bypassing the proxy) to spoof both the protocol and host seen by the application. Affected Versions fastify <= 5.8.2 Impact Applications using request.protocol or request.host for security decisions (HTTPS enforcement, secure cookie flags, CSRF origin checks, URL construction, host-based routing) are affected when trustProxy is configured with a restrictive trust function. When trustProxy: true (trust everything), both host and protocol trust all forwarded headers — this is expected behavior. The vulnerability only manifests with restrictive trust configurations. It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-3635 since 03/06/2026. The exploitation appears to be difficult. Access to the local network is required for this attack to succeed. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit. Upgrading to version 5.8.3 eliminates this vulnerability. Productinfo Name Fastify Version 5.8.0 5.8.1 5.8.2 Website Product: https://github.com/fastify/fastify/ CPE 2.3info 🔒 🔒 🔒 CPE 2.2info 🔒 🔒 🔒 CVSSv4info VulDB Vector: 🔒 VulDB Reliability: 🔍 CVSSv3info VulDB Meta Base Score: 4.6 VulDB Meta Temp Score: 4.5 VulDB Base Score: 3.1 VulDB Temp Score: 3.0 VulDB Vector: 🔒 VulDB Reliability: 🔍 CNA Base Score: 6.1 CNA Vector (openjs): 🔒 CVSSv2info Vector Complexity Authentication Confidentiality Integrity Availability Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock Unlock VulDB Base Score: 🔒 VulDB Temp Score: 🔒 VulDB Reliability: 🔍 Exploitinginfo Class: Less trusted source CWE: CWE-348 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Partially Availability: 🔒 Status: Not defined 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: Fastify 5.8.3 Timelineinfo 03/06/2026 CVE reserved 03/23/2026 +17 days Advisory disclosed 03/23/2026 +0 days VulDB entry created 03/23/2026 +0 days VulDB entry last update Sourcesinfo Product: github.com Advisory: GHSA-444r-cwp2-x5xf Status: Confirmed CVE: CVE-2026-3635 (🔒) GCVE (CVE): GCVE-0-2026-3635 GCVE (VulDB): GCVE-100-352519 Entryinfo Created: 03/23/2026 15:34 Changes: 03/23/2026 15:34 (64) Complete: 🔍 Cache ID: 99:741:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸