Bug 2547112 (CVE-2026-106445)

Summary: CVE-2026-106445 handlebars: Handlebars: JavaScript Injection via Own Property Check Bypass
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: aazores, abarbaro, abrianik, abuckta, alizardo, ataylor, bbrownin, cmah, csuconic, dbosanac, dbruscin, dkuc, doconnor, dschmidt, eaguilar, ebaron, ehugonne, fmariani, gbenhaim, ggrzybek, gmalinko, gotiwari, gparvin, gtully, ikhan, janstey, jbalunas, jchui, jhe, jhorak, jlanda, jmatsuok, jraez, jreimann, jsherman, jtolenti, jwon, kshier, ktsao, kvanderr, lchilton, mcarlett, mdessi, mrizzi, mvyas, nboldt, niyer, oaljalju, orabin, parichar, pcattana, pjindal, psrna, rbobbitt, rgemmell, rgodfrey, rhaigner, rhel-process-autobot, rstepani, sdawley, sfeifer, simaishi, stcannon, tasato, tbish, tcunning, tlavocat, tsze, twaugh, watson-tool-maintainers, yfang, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Handlebars. The lookupProperty own-property check returns Function.prototype.constructor before the prototype-method deny list is applied. When an attacker can render a controlled template with allowProtoMethodsByDefault enabled and an accessible function in the template context, arbitrary JavaScript can execute with the application process privileges.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2548542, 2548545, 2548546, 2548548, 2548552, 2548543, 2548544, 2548547, 2548550, 2548554    
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Description OSIDB Bzimport 2026-10-06 19:54:03 UTC 
Handlebars provides the power necessary to let users build semantic templates. From 4.0.0 until 4.7.10, Handlebars lookupProperty returns Function.prototype.constructor before applying the prototype-access deny list because constructor is an own property of Function.prototype. When an attacker can render a controlled template with allowProtoMethodsByDefault enabled and an accessible function in the template context, the template can traverse from that function through its prototype to Function.prototype and then obtain the Function constructor through the own-property bypass. This permits attacker-controlled JavaScript to execute with the server application's privileges. This issue is fixed in version 4.7.10.