Bug 2509801 (CVE-2026-18446)

Summary:	CVE-2026-18446 fast-uri: fast-uri: Host confusion vulnerability via backslash in URI authority
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	aazores, abarbaro, abrianik, akostadi, alizardo, amasferr, anpicker, anthomas, aruklets, ataylor, bbrownin, brasmith, cdrage, cmah, cochase, dbruscin, dhanak, dmayorov, doconnor, dranck, drosa, dschmidt, dsimansk, dymurray, eaguilar, ebaron, ehelms, ehugonne, ewittman, gbenhaim, ggainey, ggrzybek, gparvin, hasun, ibolton, janstey, jchui, jfula, jhe, jlanda, jlledo, jmatsuok, jmatthew, jmontleo, jowilson, jpasqual, jraez, jtolenti, juwatts, jwong, kaycoth, kingland, kshier, ktsao, kvanderr, mdellweg, mhulan, mnovotny, mstipich, nboldt, nipatil, niyer, nmoumoul, nyancey, oaljalju, omaciel, ometelka, osousa, pantinor, parichar, pcreech, pgaikwad, pjindal, psrna, ptisnovs, rchan, rexwhite, rhaigner, rhel-process-autobot, rjohnson, rkubis, rushinde, sausingh, sdawley, simaishi, slucidi, smallamp, sseago, stcannon, sthirugn, syedriko, tasato, teagle, tmalecek, tsedmik, ttakamiy, twaugh, watson-tool-maintainers, xdharmai, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in fast-uri. This vulnerability arises because fast-uri incorrectly parses Uniform Resource Identifiers (URIs) when a backslash is used in place of a forward slash to introduce the authority component. This discrepancy with Node's native WHATWG URL parser can lead to host confusion. A remote attacker could exploit this to bypass security policies, such as allowlists or Server-Side Request Forgery (SSRF) filters, potentially redirecting applications to unintended hosts.	Story Points:	---
Clone Of:		Environment:
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-07-31 15:01:26 UTC

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.