Bug 2556005 (CVE-2026-110306)

Summary:	CVE-2026-110306 fast-uri: fast-uri: Cross-Site Scripting via improper URI scheme decoding
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	aazores, abarbaro, abrianik, akhatavk, alizardo, anpicker, anthomas, aos-team-art-private, asdas, bbrownin, brasmith, bsmejkal, cdrage, cmah, cmyers, cochase, csuconic, dbruscin, dhanak, dnakabaa, doconnor, dpaolell, dranck, drosa, dschmidt, dsimansk, eaguilar, ebaron, ehelms, ggainey, ggrzybek, gparvin, gtully, hasun, jachapma, jbalunas, jchui, jdelft, jfula, jhe, jlanda, jmatsuok, jowilson, jpasqual, jraez, jsherman, jtolenti, jupierce, juwatts, jwong, kaycoth, kingland, kshier, ktsao, kvanderr, lchilton, lcouzens, lgarciaa, lryznaro, mbiarnes, mdellweg, mhulan, mnovotny, mreynolds, msauton, mstipich, nboldt, nmoumoul, nyancey, oaljalju, omaciel, ometelka, osousa, parichar, pcreech, pjindal, ppalepu, ppostler, prdhamdh, progier, psrna, ptisnovs, rbobbitt, rchan, rexwhite, rgemmell, rgodfrey, rhaigner, rhel-process-autobot, rjohnson, rushinde, sausingh, sdawley, sfeifer, sghai, sidsharm, simaishi, smallamp, snegrini, spichugi, stcannon, sthirugn, suppawar, syedriko, tasato, tbish, tbordaz, tlavocat, tmalecek, tsze, vashirov, vlaad, 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. The library incorrectly decodes percent-encoded characters in protocol schemes prior to validation, causing invalid or prohibited schemes to be accepted as valid. A remote attacker can exploit this vulnerability by submitting a specially crafted Uniform Resource Identifier (URI) to bypass application allowlists, potentially leading to Cross-Site Scripting (XSS) if the normalized output is rendered in a web browser.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2561704, 2561705, 2561706, 2561707, 2561708, 2561709, 2561713, 2561714, 2561716, 2561718, 2561723, 2561728, 2561730, 2561731, 2561717, 2561720
Bug Blocks:

Description OSIDB Bzimport 2026-10-20 07:21:57 UTC

fast-uri is a dependency-free RFC 3986 URI parser and serializer for Node.js. In versions before 2.4.8, from 3.0.0 through 3.1.8, and from 4.0.0 through 4.2.2, fast-uri percent-decodes the scheme component with the legacy global unescape() function before validating it, so an input whose decoded scheme is a dangerous token is emitted as a live scheme even though RFC 3986 does not allow percent-encoding in a scheme and no other parser accepts it. An application that screens dangerous schemes on the raw input and then stores or renders the normalized or resolved result can turn an inert string into an executable javascript, data, or vbscript URL, producing a stored or reflected cross-site scripting vector, and the equal() comparison treats an encoded and a plain scheme as the same, which can bypass equality-based allowlists. The issue is fixed in fast-uri 2.4.8, 3.1.9, and 4.2.3, and users should upgrade to one of these versions or later. As a workaround, reject input whose scheme part contains a percent sign, or check the parsed scheme against an allowlist after normalization and use that same parsed result rather than the raw string.