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CVE-2023-26920

fast-xml-parser vulnerable to Prototype Pollution through tag or attribute name

6.5 MediumFix available

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

1.15%Up 1.1 points since Dec 13, 2023
90%50%10%1%

What each source reports

NVD Score used 6.5

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Record
CVE-2023-26920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-1321
Updated
2026-11-02
CVE List No score

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Record
CVE-2023-26920
Updated
2026-11-02
EUVDEUVD-2023-1910 No score

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Record
EUVD-2023-1910
Updated
2026-11-03
GitHub AdvisoriesGHSA-x3cc-x39p-42qx 6.5

fast-xml-parser vulnerable to Prototype Pollution through tag or attribute name

Impact

As a part of this vulnerability, user was able to se code using __proto__ as a tag or attribute name.

const { XMLParser, XMLBuilder, XMLValidator} = require("fast-xml-parser");

let XMLdata = "<__proto__><polluted>hacked</polluted></__proto__>"

const parser = new XMLParser();
let jObj = parser.parse(XMLdata);

console.log(jObj.polluted) // should return hacked

Patches

The problem has been patched in v4.1.2

Workarounds

User can check for "proto" in the XML string before parsing it to the parser.

References

https://gist.github.com/Sudistark/a5a45bd0804d522a1392cb5023aa7ef7

Record
GHSA-x3cc-x39p-42qx
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-1321
Updated
2026-11-02
OSVCVE-2021-26920 6.5

In the Druid ingestion system, the InputSource is used for reading data from a certain data source. However, the HTTP InputSource allows authenticated users to read data from other sources than intended, such as the local file system, with the privileges of the Druid server process. This is not an elevation of privilege when users access Druid directly, since Druid also provides the Local InputSource, which allows the same level of access. But it is problematic when users interact with Druid indirectly through an application that allows users to specify the HTTP InputSource, but not the Local InputSource. In this case, users could bypass the application-level restriction by passing a file URL to the HTTP InputSource.

Record
CVE-2021-26920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2023-26920 6.5

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Record
DEBIAN-CVE-2023-26920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
Show 8 moreShow less
OSVGHSA-793h-6f7r-6qvm 6.5

Druid ingestion system Authenticated users can read data from other sources than intended

In the Druid ingestion system, the InputSource is used for reading data from a certain data source. However, the HTTP InputSource allows authenticated users to read data from other sources than intended, such as the local file system, with the privileges of the Druid server process. This is not an elevation of privilege when users access Druid directly, since Druid also provides the Local InputSource, which allows the same level of access. But it is problematic when users interact with Druid indirectly through an application that allows users to specify the HTTP InputSource, but not the Local InputSource. In this case, users could bypass the application-level restriction by passing a file URL to the HTTP InputSource.

Record
GHSA-793h-6f7r-6qvm
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-863
Updated
2026-11-02
OSVGHSA-x3cc-x39p-42qx 6.5

fast-xml-parser vulnerable to Prototype Pollution through tag or attribute name

Impact

As a part of this vulnerability, user was able to se code using __proto__ as a tag or attribute name.

const { XMLParser, XMLBuilder, XMLValidator} = require("fast-xml-parser");

let XMLdata = "<__proto__><polluted>hacked</polluted></__proto__>"

const parser = new XMLParser();
let jObj = parser.parse(XMLdata);

console.log(jObj.polluted) // should return hacked

Patches

The problem has been patched in v4.1.2

Workarounds

User can check for "proto" in the XML string before parsing it to the parser.

References

https://gist.github.com/Sudistark/a5a45bd0804d522a1392cb5023aa7ef7

Record
GHSA-x3cc-x39p-42qx
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-1321
Updated
2026-11-02
OSVUBUNTU-CVE-2023-26920 6.5

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Record
UBUNTU-CVE-2023-26920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVCLSA-2026-1781744123 No score

TuxCare security update for fast-xml-parser (2 CVEs)

TuxCare rebuilt fast-xml-parser to address 2 CVEs. Fixed in 3.19.0-tuxcare.1.

Record
CLSA-2026-1781744123
Updated
2026-11-02
OSVCLSA-2026-1781744124 No score

TuxCare security update for fast-xml-parser (2 CVEs)

TuxCare rebuilt fast-xml-parser to address 2 CVEs. Fixed in 3.17.5-tuxcare.1.

Record
CLSA-2026-1781744124
Updated
2026-11-02
OSVCLSA-2026-1781744131 No score

TuxCare security update for fast-xml-parser (2 CVEs)

TuxCare rebuilt fast-xml-parser to address 2 CVEs. Fixed in 3.14.0-tuxcare.1.

Record
CLSA-2026-1781744131
Updated
2026-11-02
OSV No score

fast-xml-parser before 4.1.2 allows proto for Prototype Pollution.

Record
CVE-2023-26920
Updated
2026-11-02
OSVROOT-APP-NPM-CVE-2023-26920 No score

CVE-2023-26920 in @rootio/fast-xml-parser - Patched by Root

Root has patched CVE-2023-26920 in the @rootio/fast-xml-parser package for Root:npm. Multiple fixed versions available.

Record
ROOT-APP-NPM-CVE-2023-26920
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
fast-xml-parser
npm
before 4.1.2
4.1.2
fast-xml-parser
TuxCare:npm
From an advisory covering 2 CVEs
3.19.0-tuxcare.0 up to 3.19.0-tuxcare.1, plus listed versions
3.19.0
3.19.0-tuxcare.1
fast-xml-parser
TuxCare:npm
From an advisory covering 2 CVEs
3.17.5-tuxcare.0 up to 3.17.5-tuxcare.1, plus listed versions
3.17.5
3.17.5-tuxcare.1
fast-xml-parser
TuxCare:npm
From an advisory covering 2 CVEs
3.14.0-tuxcare.0 up to 3.14.0-tuxcare.1, plus listed versions
3.14.0
3.14.0-tuxcare.1
node-webfont
Debian:12
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-1011.4.0+dfsg2+~cs35.7.26-1111.4.0+dfsg2+~cs35.7.26-1211.4.0+dfsg2+~cs35.7.26-1311.4.0+dfsg2+~cs35.7.26-14
Show 10 moreShow less
11.4.0+dfsg2+~cs35.7.26-1511.4.0+dfsg2+~cs35.7.26-1611.4.0+dfsg2+~cs35.7.26-1811.4.0+dfsg2+~cs35.7.26-1911.4.0+dfsg2+~cs35.7.26-2011.4.0+dfsg2+~cs35.7.26-2111.4.0+dfsg2+~cs35.7.26-2211.4.0+dfsg2+~cs35.7.26-711.4.0+dfsg2+~cs35.7.26-811.4.0+dfsg2+~cs35.7.26-9
None known
node-webfont
Debian:13
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-1311.4.0+dfsg2+~cs35.7.26-1411.4.0+dfsg2+~cs35.7.26-1511.4.0+dfsg2+~cs35.7.26-1611.4.0+dfsg2+~cs35.7.26-18
Show 4 moreShow less
11.4.0+dfsg2+~cs35.7.26-1911.4.0+dfsg2+~cs35.7.26-2011.4.0+dfsg2+~cs35.7.26-2111.4.0+dfsg2+~cs35.7.26-22
None known
node-webfont
Debian:14
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-1311.4.0+dfsg2+~cs35.7.26-1411.4.0+dfsg2+~cs35.7.26-1511.4.0+dfsg2+~cs35.7.26-1611.4.0+dfsg2+~cs35.7.26-18
Show 4 moreShow less
11.4.0+dfsg2+~cs35.7.26-1911.4.0+dfsg2+~cs35.7.26-2011.4.0+dfsg2+~cs35.7.26-2111.4.0+dfsg2+~cs35.7.26-22
None known
org.apache.druid:druid-core
Maven
From an advisory covering 2 CVEs
before 0.21.0, plus listed versions
0.14.0-incubating0.14.1-incubating0.14.2-incubating0.15.0-incubating0.15.1-incubating
Show 10 moreShow less
0.16.0-incubating0.16.1-incubating0.17.00.17.10.18.00.18.10.19.00.20.00.20.10.20.2
0.21.0
fast-xml-parser
npm
From an advisory covering 2 CVEs
before 4.1.2
4.1.2
@rootio/fast-xml-parser
Root:npm
before 3.21.1-root.io.1
3.21.1-root.io.1
Show 5 moreShow less
Affected packages
PackageAffectedFixed
fast-xml-parser
Root:npm
before 3.21.1-aikido.1
3.21.1-aikido.1
node-webfont
Ubuntu:24.04:LTS
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-7ubuntu1
None known
node-webfont
Ubuntu:25.10
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-1011.4.0+dfsg2+~cs35.7.26-13ubuntu2
None known
node-webfont
Ubuntu:26.10
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-1811.4.0+dfsg2+~cs35.7.26-19
None known
node-webfont
Ubuntu:26.04:LTS
All versions, plus listed versions
11.4.0+dfsg2+~cs35.7.26-13ubuntu211.4.0+dfsg2+~cs35.7.26-1411.4.0+dfsg2+~cs35.7.26-1511.4.0+dfsg2+~cs35.7.26-16build111.4.0+dfsg2+~cs35.7.26-18
None known

History

History
RecordedChangedSources
affected, facts
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2023-26920 is a medium vulnerability (CVSS 6.5) in Naturalintelligence Fast Xml Parser, published July 2, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.15%, the 67th percentile. Fixed in fast-xml-parser 4.1.2.

References

Show 15 moreShow less
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