Fast Uri
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Host-parsing ambiguity in fast-uri allows attackers to silently bypass SSRF denylists, redirect allowlists, and proxy routing rules by submitting URLs containing unbalanced authority brackets. Affected versions 2.4.5, 3.1.6, and 4.1.3 of the Fastify ecosystem URI parsing library return the malformed bracket-containing string as the host without raising an error, while Node.js's URL implementation and downstream HTTP clients resolve the same string to an entirely different host. Any application that reads the fast-uri-parsed host to enforce a security policy, then passes the original URL to an HTTP client, evaluates its controls against a string that is never the host the request actually reaches.
URI authority injection in fast-uri allows an attacker-supplied port value containing delimiter characters to demote the intended host to userinfo and redirect the parsed authority to an attacker-controlled hostname, bypassing downstream re-validation because both fast-uri and Node.js's built-in URL parser silently accept the malformed output as well-formed. Applications in the Fastify ecosystem that build URIs from parts — passing untrusted data into the port field of a URI object through serialize, normalize, or equal — on fast-uri versions before 2.4.6, 3.1.7, or 4.1.4 are affected. No public exploit has been identified at time of analysis, and the CVE is not listed in CISA KEV; vendor-released patches are available across all three active release lines.
Server-side request forgery and address-policy bypass in fast-uri, the Node.js URI parser used widely in the fastify ecosystem, allows remote unauthenticated attackers to redirect outbound requests from a target application to local or private IPv6 addresses by submitting crafted bracketed IPv6 literals with invalid trailing characters. The custom IPv6 parser silently normalizes malformed literals - collapsing some to the unspecified address (loopback) and others to private-range addresses - and returns no error on the parsed result, defeating any application-level error checking. No public exploit code or CISA KEV listing has been identified at time of analysis, but the attack requires no special privileges and low complexity, making automated exploitation plausible against any exposed application that normalizes untrusted URLs through an affected fast-uri version.
Parsing and serialization inconsistency in fast-uri, the Node.js URI parser core to the Fastify ecosystem, allows network-accessible, unauthenticated attackers to supply percent-encoded slashes in the scheme component, causing the library to report host as undefined during parsing while serialization emits a network-path reference with an attacker-controlled authority. Applications that allowlist requests on the parsed host value, or that treat a no-authority parse result as safe to resolve against a base URI, are bypassed - enabling server-side request forgery, off-site redirects, and address-policy evasion. No public exploit has been identified at time of analysis, but the CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms exploitation requires no authentication and no special configuration, making affected deployments an immediate upgrade priority.
Double-decoding of percent-encoded hostnames in fast-uri (Node.js URI parser) creates a server-side request forgery and host-policy bypass primitive in versions 2.4.1-2.4.4, 3.1.2-3.1.5, and 4.0.0-4.1.2. The library decodes percent escapes once during hostname parsing and again during authority recomposition, so a single normalize or resolve call on a doubly-encoded input can silently resolve to a different network destination - including loopback addresses - than the encoded form represents. Any application layer sitting fast-uri in front of outbound routing guards, redirect allow-lists, or host-policy checks is therefore vulnerable to SSRF. This is an incomplete-fix variant of CVE-2026-6322; no public exploit code or active exploitation (CISA KEV) has been identified at time of analysis.
Host confusion in fast-uri, a Node.js URI parser in the Fastify ecosystem, allows policy bypass by exploiting inconsistent host canonicalization between the library's own entry points. When a scheme-relative reference (e.g., //unicode-host.example/path) is passed without an explicit scheme, fast-uri's parse, normalize, and equal functions return the host verbatim, while resolve canonicalizes it to ASCII/Punycode - meaning the same input yields different host values depending on which API is called. An application that extracts a host for an allowlist check via one code path and then resolves the URI via another can be tricked into approving one host while the actual request is dispatched to a different one. No public exploit exists and CISA KEV listing is absent, but the EPSS-independent integrity impact (CVSS I:H) is real in applications relying on fast-uri for security-critical URI validation. Fixed versions are 2.4.5, 3.1.6, and 4.1.3.
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.
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 2.4.2 and the 3.x line up to 3.1.3) allows remote attackers to smuggle a different host past allowlist, denylist, SSRF, loopback, and redirect-validation checks by using a literal backslash. Because fast-uri does not treat U+005C as an authority delimiter while Node's native WHATWG URL parser (used by fetch, undici, and the http/https clients) normalizes backslash to forward slash for special schemes, the two parsers disagree on the host, enabling requests to be steered to cloud metadata, loopback, or internal endpoints. There is no public exploit identified at time of analysis, but the flaw is trivially triggerable in affected deployments and openjsf has published a fix.
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 remote attackers defeat denylists, loopback filters, redirect validation, and SSRF/proxy-routing controls by supplying Unicode (IDN) hostnames. Because fast-uri's IDN path invokes a non-existent helper on the global URL constructor, it leaves the host in raw Unicode form while normalize() and equal() report a host that differs from what Node's WHATWG URL or fetch ultimately resolve, producing a parser-differential bypass. No public exploit is identified at time of analysis, but the bypass is trivially reproducible and primarily enables SSRF-style integrity attacks.
Authority confusion in fast-uri JavaScript library allows remote attackers to bypass URL validation security controls. The normalize() function improperly decodes percent-encoded at-signs (%40) in hostnames, then re-serializes them as raw userinfo delimiters, causing URLs like 'http://trusted.com%40evil.com' to resolve to 'evil.com' instead of 'trusted.com'. Applications using fast-uri to validate URLs against allowlists or for redirect validation can be tricked into connecting to attacker-controlled domains. CVSS 7.5 (AV:N/AC:L/PR:N/UI:N) indicates trivial remote exploitation with no authentication. EPSS data not available; no confirmed active exploitation (not in CISA KEV). Vendor patch released in version 3.1.2.
Path normalization bypass in fast-uri 3.1.0 and earlier allows remote attackers to circumvent path-based access controls through percent-encoded path traversal sequences. The normalize() and equal() functions decode URL-encoded separators (%2F) and dot segments (%2E) before applying normalization rules, causing distinct URIs to collapse onto identical normalized paths. Applications relying on fast-uri for URL validation in authorization checks can be tricked into allowing access to restricted resources. EPSS exploitation probability not yet calculated given recent disclosure; no active exploitation confirmed (not in CISA KEV), but attack vector is trivial (CVSS AV:N/AC:L/PR:N/UI:N) and patch is available in version 3.1.1.
The mailto scheme parser added to fast-uri 4.1.3 (and still present in 4.1.4) compares query field names against the reserved names 'to', 'subject' and 'body' while they are still percent-encoded, then decodes them only when storing them as generic headers — so a percent-encoded spelling of a reserved field is invisible to that check but is written back out as the literal field name during serialization. Any application built on Fastify, ajv or similar Node.js stacks that parses a mailto URI, validates, logs or displays the recipient list, and then re-serializes it with fast-uri before sending can be tricked into delivering mail to an attacker-chosen address, with subject and body content smuggled across the same roundtrip. The flaw is rated 4.8 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N, CWE-172 Encoding Error) and is fixed in fast-uri 4.1.5.
Host allowlist and denylist bypass in fast-uri, the dependency-free RFC 3986 URI parser used by Fastify and ajv, affects releases before 2.4.7, 3.0.0 through 3.1.7, and 4.0.0 through 4.1.4. Because the library lowercases the host before percent-decoding it, an encoded uppercase octet such as %41 survives as a literal 'A', and in scheme-relative references like //host the canonicalization pass that would normally repair this never runs, so parse, normalize, and equal disagree about the same hostname. Any application that makes a case-sensitive host decision on fast-uri output — a host allowlist or denylist comparing the parsed host, or code relying on equal — can be steered past that check while the evading spelling still resolves to the gated host in DNS and HTTP. Exploitation status: no public exploit identified at time of analysis.
Host-parsing ambiguity in fast-uri allows attackers to silently bypass SSRF denylists, redirect allowlists, and proxy routing rules by submitting URLs containing unbalanced authority brackets. Affected versions 2.4.5, 3.1.6, and 4.1.3 of the Fastify ecosystem URI parsing library return the malformed bracket-containing string as the host without raising an error, while Node.js's URL implementation and downstream HTTP clients resolve the same string to an entirely different host. Any application that reads the fast-uri-parsed host to enforce a security policy, then passes the original URL to an HTTP client, evaluates its controls against a string that is never the host the request actually reaches.
URI authority injection in fast-uri allows an attacker-supplied port value containing delimiter characters to demote the intended host to userinfo and redirect the parsed authority to an attacker-controlled hostname, bypassing downstream re-validation because both fast-uri and Node.js's built-in URL parser silently accept the malformed output as well-formed. Applications in the Fastify ecosystem that build URIs from parts — passing untrusted data into the port field of a URI object through serialize, normalize, or equal — on fast-uri versions before 2.4.6, 3.1.7, or 4.1.4 are affected. No public exploit has been identified at time of analysis, and the CVE is not listed in CISA KEV; vendor-released patches are available across all three active release lines.
Server-side request forgery and address-policy bypass in fast-uri, the Node.js URI parser used widely in the fastify ecosystem, allows remote unauthenticated attackers to redirect outbound requests from a target application to local or private IPv6 addresses by submitting crafted bracketed IPv6 literals with invalid trailing characters. The custom IPv6 parser silently normalizes malformed literals - collapsing some to the unspecified address (loopback) and others to private-range addresses - and returns no error on the parsed result, defeating any application-level error checking. No public exploit code or CISA KEV listing has been identified at time of analysis, but the attack requires no special privileges and low complexity, making automated exploitation plausible against any exposed application that normalizes untrusted URLs through an affected fast-uri version.
Parsing and serialization inconsistency in fast-uri, the Node.js URI parser core to the Fastify ecosystem, allows network-accessible, unauthenticated attackers to supply percent-encoded slashes in the scheme component, causing the library to report host as undefined during parsing while serialization emits a network-path reference with an attacker-controlled authority. Applications that allowlist requests on the parsed host value, or that treat a no-authority parse result as safe to resolve against a base URI, are bypassed - enabling server-side request forgery, off-site redirects, and address-policy evasion. No public exploit has been identified at time of analysis, but the CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms exploitation requires no authentication and no special configuration, making affected deployments an immediate upgrade priority.
Double-decoding of percent-encoded hostnames in fast-uri (Node.js URI parser) creates a server-side request forgery and host-policy bypass primitive in versions 2.4.1-2.4.4, 3.1.2-3.1.5, and 4.0.0-4.1.2. The library decodes percent escapes once during hostname parsing and again during authority recomposition, so a single normalize or resolve call on a doubly-encoded input can silently resolve to a different network destination - including loopback addresses - than the encoded form represents. Any application layer sitting fast-uri in front of outbound routing guards, redirect allow-lists, or host-policy checks is therefore vulnerable to SSRF. This is an incomplete-fix variant of CVE-2026-6322; no public exploit code or active exploitation (CISA KEV) has been identified at time of analysis.
Host confusion in fast-uri, a Node.js URI parser in the Fastify ecosystem, allows policy bypass by exploiting inconsistent host canonicalization between the library's own entry points. When a scheme-relative reference (e.g., //unicode-host.example/path) is passed without an explicit scheme, fast-uri's parse, normalize, and equal functions return the host verbatim, while resolve canonicalizes it to ASCII/Punycode - meaning the same input yields different host values depending on which API is called. An application that extracts a host for an allowlist check via one code path and then resolves the URI via another can be tricked into approving one host while the actual request is dispatched to a different one. No public exploit exists and CISA KEV listing is absent, but the EPSS-independent integrity impact (CVSS I:H) is real in applications relying on fast-uri for security-critical URI validation. Fixed versions are 2.4.5, 3.1.6, and 4.1.3.
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.
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 2.4.2 and the 3.x line up to 3.1.3) allows remote attackers to smuggle a different host past allowlist, denylist, SSRF, loopback, and redirect-validation checks by using a literal backslash. Because fast-uri does not treat U+005C as an authority delimiter while Node's native WHATWG URL parser (used by fetch, undici, and the http/https clients) normalizes backslash to forward slash for special schemes, the two parsers disagree on the host, enabling requests to be steered to cloud metadata, loopback, or internal endpoints. There is no public exploit identified at time of analysis, but the flaw is trivially triggerable in affected deployments and openjsf has published a fix.
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 remote attackers defeat denylists, loopback filters, redirect validation, and SSRF/proxy-routing controls by supplying Unicode (IDN) hostnames. Because fast-uri's IDN path invokes a non-existent helper on the global URL constructor, it leaves the host in raw Unicode form while normalize() and equal() report a host that differs from what Node's WHATWG URL or fetch ultimately resolve, producing a parser-differential bypass. No public exploit is identified at time of analysis, but the bypass is trivially reproducible and primarily enables SSRF-style integrity attacks.
Authority confusion in fast-uri JavaScript library allows remote attackers to bypass URL validation security controls. The normalize() function improperly decodes percent-encoded at-signs (%40) in hostnames, then re-serializes them as raw userinfo delimiters, causing URLs like 'http://trusted.com%40evil.com' to resolve to 'evil.com' instead of 'trusted.com'. Applications using fast-uri to validate URLs against allowlists or for redirect validation can be tricked into connecting to attacker-controlled domains. CVSS 7.5 (AV:N/AC:L/PR:N/UI:N) indicates trivial remote exploitation with no authentication. EPSS data not available; no confirmed active exploitation (not in CISA KEV). Vendor patch released in version 3.1.2.
Path normalization bypass in fast-uri 3.1.0 and earlier allows remote attackers to circumvent path-based access controls through percent-encoded path traversal sequences. The normalize() and equal() functions decode URL-encoded separators (%2F) and dot segments (%2E) before applying normalization rules, causing distinct URIs to collapse onto identical normalized paths. Applications relying on fast-uri for URL validation in authorization checks can be tricked into allowing access to restricted resources. EPSS exploitation probability not yet calculated given recent disclosure; no active exploitation confirmed (not in CISA KEV), but attack vector is trivial (CVSS AV:N/AC:L/PR:N/UI:N) and patch is available in version 3.1.1.
The mailto scheme parser added to fast-uri 4.1.3 (and still present in 4.1.4) compares query field names against the reserved names 'to', 'subject' and 'body' while they are still percent-encoded, then decodes them only when storing them as generic headers — so a percent-encoded spelling of a reserved field is invisible to that check but is written back out as the literal field name during serialization. Any application built on Fastify, ajv or similar Node.js stacks that parses a mailto URI, validates, logs or displays the recipient list, and then re-serializes it with fast-uri before sending can be tricked into delivering mail to an attacker-chosen address, with subject and body content smuggled across the same roundtrip. The flaw is rated 4.8 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N, CWE-172 Encoding Error) and is fixed in fast-uri 4.1.5.
Host allowlist and denylist bypass in fast-uri, the dependency-free RFC 3986 URI parser used by Fastify and ajv, affects releases before 2.4.7, 3.0.0 through 3.1.7, and 4.0.0 through 4.1.4. Because the library lowercases the host before percent-decoding it, an encoded uppercase octet such as %41 survives as a literal 'A', and in scheme-relative references like //host the canonicalization pass that would normally repair this never runs, so parse, normalize, and equal disagree about the same hostname. Any application that makes a case-sensitive host decision on fast-uri output — a host allowlist or denylist comparing the parsed host, or code relying on equal — can be steered past that check while the evading spelling still resolves to the gated host in DNS and HTTP. Exploitation status: no public exploit identified at time of analysis.