Bug 2521779 (CVE-2026-75975)

Summary: CVE-2026-75975 fast-uri: fast-uri: Server-side request forgery via malformed IPv6 normalization
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. Its custom parser for bracketed IPv6 literals does not fully validate the IPv6 grammar, allowing invalid trailing text in an authority to be silently discarded. This can lead to a malformed, attacker-controlled host being normalized into a different, valid IPv6 destination, such as a local or private IPv6 target. An application normalizing untrusted URLs before outbound requests, redirects, or proxy routing could be redirected, resulting in a server-side request forgery (SSRF) and address-policy bypass.
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Description OSIDB Bzimport 2026-08-24 10:11:30 UTC 
fast-uri is a URI parser for Node.js. Its custom parser for bracketed IPv6 literals does not validate the complete IPv6 grammar, so invalid trailing text in an authority can be silently discarded and a malformed attacker-controlled host is turned into a different valid IPv6 destination. For example, a bracketed literal with invalid trailing characters is normalized to the unspecified address, which a Node HTTP client then connects to a local service over loopback, and other malformed literals collapse to private-range addresses. No error is set on the parsed result, so an application checking the error field cannot detect the rewrite. An application that normalizes untrusted URLs before outbound requests, redirects, proxy routing, or address-policy enforcement can be redirected to a local or private IPv6 target, giving a server-side request forgery and address-policy bypass primitive. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which validate bracketed IP literals against the full grammar and mark malformed literals as authority errors. Users should upgrade to a patched version.