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CVE-2018-20843

28
FAUCET Score

CVE-2018-20843 describes a denial-of-service vulnerability in libexpat versions prior to 2.2.7, affecting various products including Canonical, Debian, Fedora, and Oracle. An unauthenticated attacker can exploit this by submitting XML input with numerous colons in XML names, causing the parser to consume excessive RAM and CPU resources. With a CVSS score of 7.5 (High), this vulnerability presents a significant availability risk due to its low attack complexity and network-based vector. There is currently no evidence of active exploitation, nor are there publicly available exploits in Metasploit or ExploitDB, and it has received minimal community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
< 2.2.7CPE matchmatch criteria
cpe:2.3:a:libexpat_project:libexpat:*:*:*:*:*:*:*:*
12.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:12.04:*:*:*:-:*:*:*
14.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:esm:*:*:*
16.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
18.04CPE matchmatch criteria
cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
7.11%
Probability of exploitation in next 30 days
EPSS Percentile
93.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0711 is in the 89th percentile among its peer group of 51,553 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (29)

github_advisorypatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: 16964-16820Fixed in: 2.2.6-4
microsoftpatch availablevia msrc
Product: CBL Mariner 1.0 ARMFixed in: 2.2.6-4
microsoftpatch availablevia msrc
Product: cm1 expat 2.2.6-4 on CBL Mariner 1.0Fixed in: 2.2.6-4
microsoftpatch availablevia msrc
Product: CBL Mariner 1.0 x64Fixed in: 2.2.6-4
oraclepatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-mod_http2-0:1.15.7-3.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-mod_jk-0:1.2.48-4.redhat_1.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-mod_md-1:2.0.8-24.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-mod_security-0:2.9.2-51.GA.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-nghttp2-0:1.39.2-25.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-curl-0:7.64.1-36.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-httpd-0:2.4.37-57.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_cluster-native-0:1.3.14-4.Final_redhat_2.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_http2-0:1.15.7-3.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_jk-0:1.2.48-4.redhat_1.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_md-1:2.0.8-24.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-mod_security-0:2.9.2-51.GA.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-nghttp2-0:1.39.2-25.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 7Fixed in: jbcs-httpd24-openssl-pkcs11-0:0.4.10-7.jbcs.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: expat-0:2.1.0-12.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: mingw-expat-0:2.2.4-5.el8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: expat-0:2.2.5-4.el8
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8.2 Advanced Update SupportFixed in: expat-0:2.2.10-1.el8_2
View patch
redhatpatch availablevia redhat_api
Product: Red Hat OpenShift DoFixed in: openshiftdo/odo-init-image-rhel7:1.1.3-2
View patch
redhatpatch availablevia redhat_api
Product: Text-Only JBCSFixed in: expat
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-curl-0:7.64.1-36.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-mod_cluster-native-0:1.3.14-4.Final_redhat_2.jbcs.el6
View patch
redhatpatch availablevia redhat_api
Product: JBoss Core Services on RHEL 6Fixed in: jbcs-httpd24-httpd-0:2.4.37-57.jbcs.el6
View patch

Vendor Advisories (3)

microsoft2020-Aug/CVE-2018-20843

CVE-2018-20843

Aug 11, 2020
redhatCVE-2018-20843Moderate

expat: large number of colons in input makes parser consume high amount of resources, leading to DoS

Jun 24, 2019
microsoft2019-Jun/CVE-2018-20843Important

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).

Jun 11, 2019

References

lists.opensuse.org / opensuse-security-announce/2019-07/msg00039.html
Mailing ListThird Party Advisory
bugs.chromium.org / p/oss-fuzz/issues/detail
Issue TrackingThird Party Advisory
github.com / libexpat/libexpat/blob/R_2_2_7/expat/Changes
Release NotesThird Party Advisory
github.com / libexpat/libexpat/issues/186
Issue TrackingPatchThird Party Advisory
github.com / libexpat/libexpat/pull/262
ExploitPatchThird Party Advisory
github.com / libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d00c4ff6
PatchThird Party Advisory
lists.debian.org / debian-lts-announce/2019/06/msg00028.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/CEJJSQSG3KSUQY4FPVHZ7ZTT7FORMFVD
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/IDAUGEB3TUP6NEKJDBUBZX7N5OAUOOOK
seclists.org / bugtraq/2019/Jun/39
Mailing ListThird Party Advisory
security.gentoo.org / glsa/201911-08
Third Party Advisory
security.netapp.com / advisory/ntap-20190703-0001
Third Party Advisory
support.f5.com / csp/article/K51011533
Third Party Advisory
usn.ubuntu.com / 4040-1
Third Party Advisory
usn.ubuntu.com / 4040-2
Third Party Advisory
debian.org / security/2019/dsa-4472
Third Party Advisory
oracle.com / security-alerts/cpuapr2020.html
PatchThird Party Advisory
oracle.com / security-alerts/cpuApr2021.html
PatchThird Party Advisory
oracle.com / security-alerts/cpuoct2020.html
PatchThird Party Advisory
oracle.com / security-alerts/cpuoct2021.html
PatchThird Party Advisory
tenable.com / security/tns-2021-11
Third Party Advisory