CVE-2018-20843

CVE-2018-20843 is a high-severity vulnerability in Libexpat Project Libexpat with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-611.

Key facts

• Severity: High (CVSS 3.x base score 7.5)
• CVSS v2: 7.8
• EPSS exploit prediction: 7% (93rd percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-611
• Affected product: Libexpat Project Libexpat
• Published: 2019-06-24
• Last modified: 2026-06-17

Description

In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).

Frequently asked questions

What is CVE-2018-20843?

In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of colons could make the XML parser consume a high amount of RAM and CPU resources while processing (enough to be usable for denial-of-service attacks).

How severe is CVE-2018-20843?

CVE-2018-20843 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2018-20843 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 7% (93rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-20843?

CVE-2018-20843 primarily affects Libexpat Project Libexpat. In total, 19 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2018-20843?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2018-20843 published?

CVE-2018-20843 was published on 2019-06-24 and last updated on 2026-06-17.

References

• http://lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html
• https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5226
• https://github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
• https://github.com/libexpat/libexpat/issues/186
• https://github.com/libexpat/libexpat/pull/262
• https://github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
• https://lists.debian.org/debian-lts-announce/2019/06/msg00028.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEJJSQSG3KSUQY4FPVHZ7ZTT7FORMFVD/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IDAUGEB3TUP6NEKJDBUBZX7N5OAUOOOK/
• https://seclists.org/bugtraq/2019/Jun/39
• https://security.gentoo.org/glsa/201911-08
• https://security.netapp.com/advisory/ntap-20190703-0001/
• https://support.f5.com/csp/article/K51011533
• https://usn.ubuntu.com/4040-1/
• https://usn.ubuntu.com/4040-2/
• https://www.debian.org/security/2019/dsa-4472
• https://www.oracle.com/security-alerts/cpuApr2021.html
• https://www.oracle.com/security-alerts/cpuapr2020.html
• https://www.oracle.com/security-alerts/cpuoct2020.html
• https://www.oracle.com/security-alerts/cpuoct2021.html
• https://www.tenable.com/security/tns-2021-11

Affected products (19)

• cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:12.04:*:*:*:-:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:esm:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:18.10:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:19.04:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:29:*:*:*:*:*:*:*
• cpe:2.3:o:fedoraproject:fedora:30:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:leap:15.0:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:leap:15.1:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:hospitality_res_3700:*:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:http_server:12.1.3.0:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:http_server:12.2.1.4.0:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:outside_in_technology:8.5.4:*:*:*:*:*:*:*
• cpe:2.3:a:oracle:outside_in_technology:8.5.5:*:*:*:*:*:*:*
• cpe:2.3:a:tenable:nessus:*:*:*:*:*:*:*:*

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