Bug 2521777 (CVE-2026-75931)

Summary: CVE-2026-75931 fast-uri: fast-uri: Host confusion via skipped IDN canonicalization
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: abarbaro, akhatavk, alizardo, anpicker, anthomas, aos-team-art-private, aruklets, asdas, ataylor, bbrownin, bparees, brasmith, cdrage, cochase, dbruscin, dhanak, doconnor, dpaolell, dranck, drosa, dschmidt, dsimansk, dymurray, ehelms, ehugonne, ewittman, ggainey, gparvin, hasun, ibolton, janstey, jchui, jdelft, jfula, jhe, jlanda, jmatthew, jmontleo, jowilson, jpasqual, jupierce, juwatts, jwong, kaycoth, kingland, kshier, ktsao, kvanderr, lchilton, lgarciaa, mbiarnes, mdellweg, mhulan, mnovotny, mstipich, nboldt, nipatil, nmoumoul, nyancey, oaljalju, omaciel, ometelka, osousa, pantinor, pcreech, pgaikwad, pjindal, ppalepu, ppostler, prdhamdh, psrna, ptisnovs, rchan, rexwhite, rhaigner, rhel-process-autobot, rjohnson, rkubis, rushinde, sausingh, sdawley, sfeifer, sghai, sidsharm, simaishi, slucidi, smallamp, sseago, stcannon, sthirugn, suppawar, syedriko, teagle, tmalecek, ttakamiy, vlaad, watson-tool-maintainers, xdharmai, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in fast-uri, a URI parser for Node.js. This vulnerability arises because the parser fails to consistently convert internationalized domain names (IDN) to their standard ASCII form when processing scheme-relative references. This inconsistency can lead to host confusion, where an application might validate a URI against a security policy using one hostname, but then resolve to a different, potentially malicious, hostname. This discrepancy could allow an attacker to bypass security policies and access unauthorized resources.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-24 09:51:25 UTC 
fast-uri is a URI parser for Node.js. It canonicalizes a host to its ASCII form only when the input carries an explicit scheme, so a scheme-relative reference such as a host preceded by two slashes is returned with its host verbatim and no error set. As a result fast-uri's own entry points disagree with each other: parse, resolve, normalize, and equal can yield different hosts for the same input depending only on whether a scheme is written out, and equal can return opposite verdicts for the same pair of hosts. An application that extracts a host with fast-uri to check it against a policy list and then resolves the same reference can make its decision on one host while the destination is another, enabling host confusion and policy bypass. The affected versions are 2.4.2 up to but not including 2.4.5, 3.1.3 up to but not including 3.1.6, and 4.0.1 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which canonicalize the host consistently across the resolve path. Users should upgrade to a patched version.