CVE-2026-33808 | fastify express up to 4.0.4 interpretation conflict

VDB-357695 · CVE-2026-33808 · GCVE-0-2026-33808 FASTIFY EXPRESS UP TO 4.0.4 INTERPRETATION CONFLICT HISTORYDIFFRELATEJSONXMLCTI CVSS Meta Temp Score Current Exploit Price (≈) CTI Interest Score 7.0 $0-$5k 3.13+ Summaryinfo A vulnerability identified as critical has been detected in fastify express up to 4.0.4. This affects an unknown function. The manipulation leads to interpretation conflict. This vulnerability is referenced as CVE-2026-33808. Remote exploitation of the attack is possible. No exploit is available. You should upgrade the affected component. Detailsinfo A vulnerability was found in fastify express up to 4.0.4. It has been rated as critical. This issue affects some unknown functionality. The manipulation with an unknown input leads to a interpretation conflict vulnerability. Using CWE to declare the problem leads to CWE-436. Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state. Impacted is confidentiality, integrity, and availability. The summary by CVE is: 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. It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-33808 since 03/23/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. Upgrading to version 4.0.5 eliminates this vulnerability. Productinfo Vendor fastify Name express Version 4.0.0 4.0.1 4.0.2 4.0.3 4.0.4 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 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: Interpretation conflict CWE: CWE-436 CAPEC: 🔒 ATT&CK: 🔒 Physical: No Local: No Remote: Yes 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: express 4.0.5 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-2026-33808 (🔒) GCVE (CVE): GCVE-0-2026-33808 GCVE (VulDB): GCVE-100-357695 Entryinfo Created: 04/15/2026 12:13 Changes: 04/15/2026 12:13 (65) Complete: 🔍 Cache ID: 99:F40:101 Discussion No comments yet. Languages: en. Please log in to comment. ◂ PreviousOverviewNext ▸