CVE-2026-33036
HIGHDescription
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 A 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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Moderate risk: more likely to be exploited than 53% of all known CVEs.
References
Related Vulnerabilities
Other CWE-776 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2009-1955 | High | 7.5 | 53% | - | Fix |
| CVE-2017-18640 | High | 7.5 | 27% | - | Fix |
| CVE-2019-11253 | High | 7.5 | 26% | - | Fix |
| CVE-2019-12401 | High | 7.5 | 8.5% | - | - |
| CVE-2023-20052 | Medium | 5.3 | 7.0% | - | Fix |
| CVE-2019-15903 | High | 7.5 | 6.6% | - | Fix |
Common questions
How do I fix CVE-2026-33036?
Upgrade fast-xml-parser to 5.5.6 or later.
Is CVE-2026-33036 being actively exploited?
Not that we know of. CVE-2026-33036 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.73% is the estimated probability that it will be exploited in the next 30 days. That is higher than 53% of all scored CVEs.
How severe is CVE-2026-33036?
CVE-2026-33036 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-33036 affect?
Published advisories record a fix for fast-xml-parser (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-03-23.