CVE-2026-33036: fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-33036 is a high-severity flaw (CVSS 7.5) affecting fast-xml-parser. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 replaceEnt

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 52%)
CISA exploited list	No
Weakness	CWE-776
Published	2026-03-20
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: naturalintelligence

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-20 06:16 UTCPublished CVE record published
2026-06-17 10:36 UTCUpdated Record last modified

naturalintelligence fast-xml-parser UPGRADE

Affected: >= 4.0.1 and < 5.5.6 · 4.0.0 · 4.0.0 beta3 · 4.0.0 beta4 · 4.0.0 beta5 · 4.0.0 beta6 · 4.0.0 beta7 · 4.0.0 beta8

Fixed in: 5.5.6

Safe to downgrade to: a release before 4.0.0

1. Check installed version

apt-cache policy fast-xml-parser || rpm -q fast-xml-parser || fast-xml-parser --version

2. UPGRADE to 5.5.6 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fast-xml-parser

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fast-xml-parser

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.0.0 (Debian / Ubuntu)

apt-cache madison fast-xml-parser sudo apt install fast-xml-parser=<VERSION_BEFORE_4.0.0> sudo apt-mark hold fast-xml-parser

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fast-xml-parser sudo dnf downgrade fast-xml-parser-<VERSION_BEFORE_4.0.0> sudo dnf versionlock add fast-xml-parser

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33036?

fast-xml-parser: upgrade to 5.5.6. Exact commands for each OS are on this page.

Is CVE-2026-33036 being exploited?

CVE-2026-33036 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33036 affect?

CVE-2026-33036 affects fast-xml-parser. Severity is high (CVSS 7.5). 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 e

How urgent is CVE-2026-33036?

Priority 48/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-41650 MEDIUM 6.1 UPGRADE fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks
CVE-2026-25896 CRITICAL 9.3 UPGRADE fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C+
CVE-2026-33349 MEDIUM 5.9 UPGRADE fast-xml-parser allows users to process XML from JS object without C/C++ based libraries or callbacks
CVE-2026-27942 HIGH 7.5 UPGRADE fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C+

References

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