Bug 2449458 (CVE-2026-33036)

Summary: CVE-2026-33036 fast-xml-parser: fast-xml-parser: Denial of Service via XML entity expansion bypass
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: abarbaro, abuckta, alizardo, anjoseph, anthomas, caswilli, dkuc, dschmidt, ehelms, erezende, fdeutsch, ggainey, jchui, jhe, jkoehler, jlanda, jprabhak, juwatts, kaycoth, kshier, ktsao, lphiri, manissin, mhulan, nboldt, nmoumoul, oaljalju, orabin, oramraz, osousa, pcreech, psrna, rchan, rjohnson, simaishi, smallamp, smcdonal, smullick, stcannon, stirabos, teagle, thason, tmalecek, wtam, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in fast-xml-parser. A remote attacker can exploit this vulnerability by supplying specially crafted XML input containing numeric character references or standard XML entities. This input can bypass configured entity expansion limits, leading to excessive memory allocation and high CPU usage. The primary consequence is a Denial of Service (DoS), which can crash the affected process.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2449481, 2449480    
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Description OSIDB Bzimport 2026-03-20 06:02:51 UTC 
fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks. Versions 4.0.0-beta.3 through 5.5.5 contain a bypass vulnerability where numeric character references (&#NNN;, &#xHH;) and standard XML entities completely evade the entity expansion limits (e.g., maxTotalExpansions, maxExpandedLength) added to fix CVE-2026-26278, enabling XML entity expansion Denial of Service. The root cause is that replaceEntitiesValue() in OrderedObjParser.js only enforces expansion counting on DOCTYPE-defined entities while the lastEntities loop handling numeric/standard entities performs no counting at all. An attacker supplying 1M numeric entity references like &#65; can force ~147MB of memory allocation and heavy CPU usage, potentially crashing the process—even when developers have configured strict limits. This issue has been fixed in version 5.5.6.