Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Network vector with no privileges required to submit a crafted URL; integrity-only impact reflects security control bypass without direct confidentiality or availability consequence.
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Primary rating from Vendor (openjs).
CVSS VectorVendor: openjs
Lifecycle Timeline
3DescriptionCVE.org
fast-uri before 4.1.2, 3.1.5, and 2.4.4 requires a literal double forward slash to recognize a URI authority, so a reference that uses a backslash based introducer in place of it (backslash backslash, forward slash backslash, or backslash forward slash) is parsed with no authority and folds into the path. Node's native WHATWG URL parser instead treats a backslash as interchangeable with a forward slash for special schemes, so the two parsers extract different hosts from the same input. Applications that use fast-uri to enforce host based policy such as allowlists, SSRF filtering, or redirect validation before passing the same URL into Node's URL or fetch consumers can be steered to an unintended host. Upgrade to fast-uri 4.1.2, 3.1.5, or 2.4.4.
AnalysisAI
Security filter bypass in fast-uri (before versions 4.1.2, 3.1.5, and 2.4.4) enables unauthenticated remote attackers to circumvent host-based access controls - including SSRF filters, allowlists, and redirect validators - by submitting URLs that use backslash-based authority introducers. The parser inconsistency between fast-uri and Node.js's native WHATWG URL handler causes the same crafted URL to resolve to different hosts in each parser, allowing attackers to steer downstream requests to unintended destinations. No public exploit is identified at time of analysis and this CVE does not appear in CISA KEV, though the CVSS 7.5 High rating with AV:N/AC:L/PR:N/UI:N reflects straightforward remote exploitability wherever the vulnerable application pattern exists.
Technical ContextAI
fast-uri is a URI parsing library central to the Fastify Node.js web framework ecosystem, identified by CPE cpe:2.3:a:fast-uri:fast-uri:*:*:*:*:*:*:*:*. The root cause is CWE-436 (Interpretation Conflict) - a vulnerability class where two components processing the same input derive different semantic results. fast-uri strictly requires a literal double forward slash ('//') to recognize a URI authority component; when a backslash-based sequence ('\\', '/\', or '\/') is used instead, fast-uri treats the input as having no authority and folds the remainder into the path. Node.js's native WHATWG URL parser, by contrast, follows the WHATWG URL Living Standard which explicitly treats backslash as equivalent to forward slash for 'special' URI schemes (http, https, ftp, ws, wss). This standard-compliant behavior means Node.js correctly identifies the intended host in such URLs while fast-uri does not - a textbook parser differential, a well-documented attack pattern in SSRF and open-redirect research. Applications that use fast-uri as a security enforcement gate and then pass the same URL string to Node's URL API or fetch() as the actual consumer are exposed to the discrepancy.
RemediationAI
Upgrade fast-uri to version 4.1.2, 3.1.5, or 2.4.4 as appropriate for the major version in use; these are the vendor-released patches confirmed by the OpenJS Foundation CNA via the advisory at https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7. If an immediate upgrade is not feasible, a compensating control is to preprocess user-supplied URLs before passing them to fast-uri by normalizing all backslash characters in the authority position to forward slashes - this eliminates the ambiguity the attacker exploits, though it alters URL semantics and must be validated against application behavior. Alternatively, consolidate all URL host extraction and policy enforcement onto Node's native URL parser exclusively, eliminating the parser differential entirely; this requires verifying that fast-uri is removed from the security-critical validation path. As a defense-in-depth measure independent of this fix, enforce network-level egress filtering on outbound HTTP requests so that no application-layer allowlist is the sole SSRF control - bypassing the filter should not be sufficient to reach sensitive internal endpoints.
Host-based security policy bypass in the fast-uri Node.js URI parser (versions 2.3.1 through 3.1.2 and 4.0.0) lets remot
Path normalization bypass in fast-uri 3.1.0 and earlier allows remote attackers to circumvent path-based access controls
Authority confusion in fast-uri JavaScript library allows remote attackers to bypass URL validation security controls. T
Host confusion in fast-uri, a Node.js URI parser in the Fastify ecosystem, allows policy bypass by exploiting inconsiste
Server-side request forgery and address-policy bypass in fast-uri, the Node.js URI parser used widely in the fastify eco
Double-decoding of percent-encoded hostnames in fast-uri (Node.js URI parser) creates a server-side request forgery and
Parsing and serialization inconsistency in fast-uri, the Node.js URI parser core to the Fastify ecosystem, allows networ
URI authority injection in fast-uri allows an attacker-supplied port value containing delimiter characters to demote the
Host-parsing ambiguity in fast-uri allows attackers to silently bypass SSRF denylists, redirect allowlists, and proxy ro
Host-based policy bypass in the fast-uri Node.js URI parser (versions 2.3.1 through 4.1.0, spanning the 2.x line up to 2
Same weakness CWE-436 – Interpretation Conflict
View allVendor StatusVendor
SUSE
Severity: Moderate| Product | Status |
|---|---|
| SUSE Linux Enterprise Micro 5.3 | Not-Affected |
| SUSE Linux Enterprise Micro 5.3 | Not-Affected |
| SUSE Linux Enterprise Micro 5.3 | Not-Affected |
| SUSE Linux Enterprise Micro 5.3 | Not-Affected |
| SUSE Linux Enterprise Micro 5.4 | Not-Affected |
| SUSE Linux Enterprise Micro 5.4 | Not-Affected |
| SUSE Linux Enterprise Micro 5.4 | Not-Affected |
| SUSE Linux Enterprise Micro 5.4 | Not-Affected |
| SUSE Linux Enterprise Micro 5.5 | Not-Affected |
| SUSE Linux Enterprise Micro 5.5 | Not-Affected |
| SUSE Linux Enterprise Micro 5.5 | Not-Affected |
| SUSE Linux Enterprise Micro 5.5 | Not-Affected |
| SUSE Linux Enterprise Module for SAP Applications 15 SP7 | Affected |
| SUSE Linux Enterprise Server 16.0 | Affected |
| SUSE Linux Enterprise Server 16.0 | Affected |
| SUSE Linux Enterprise Server 16.0 | Affected |
| SUSE Linux Enterprise Server 16.0 | Affected |
| SUSE Linux Enterprise Server 16.0 | Affected |
| SUSE Linux Enterprise Server 16.0 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP7 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Micro 6.0 | Not-Affected |
| SUSE Linux Micro 6.0 | Not-Affected |
| SUSE Linux Micro 6.0 | Affected |
| SUSE Linux Micro 6.0 | Not-Affected |
| SUSE Linux Micro 6.1 | Affected |
| SUSE Linux Micro 6.1 | Not-Affected |
| SUSE Linux Micro 6.1 | Not-Affected |
| SUSE Linux Micro 6.1 | Affected |
| SUSE Linux Micro 6.2 | Affected |
| SUSE Linux Micro 6.2 | Affected |
| SUSE Linux Micro 6.2 | Affected |
| SUSE Linux Micro 6.2 | Affected |
| SUSE Linux Micro 6.2 | Affected |
| SUSE Linux Micro 6.2 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| openSUSE Leap 16.0 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | Affected |
| SUSE Linux Enterprise Module for SAP Applications 15 SP3 | Affected |
| SUSE Linux Enterprise Module for SAP Applications 15 SP4 | Affected |
| SUSE Linux Enterprise Module for SAP Applications 15 SP5 | Affected |
| SUSE Linux Enterprise Module for SAP Applications 15 SP6 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP3 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP4 | Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP5 | Affected |
| openSUSE Leap Micro 5.5 | Not-Affected |
| openSUSE Leap Micro 5.5 | Not-Affected |
| openSUSE Leap Micro 5.5 | Not-Affected |
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External POC / Exploit Code
Leaving vuln.today
EUVD-2026-51553
GHSA-7p8r-x3mc-p8w7