CVE-2018-20843 — In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of...
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).
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 7.1% (30-day exploitation probability)+14
- Technical severity (high)+6
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — github.com (NIST National Vulnerability Database)
- Documented patch — github.com (NIST National Vulnerability Database)
- Documented patch — github.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
- Documented patch — www.oracle.com (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Canonical Ubuntu Linux, Debian Debian Linux, Fedoraproject Fedora…).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- Apply the fixed version or the patch documented under Remediation.
- EPSS ahead of 94% of scored CVEs: prioritize it in the patch queue.
- Search available logs for exploit probes matching the vulnerability class (injection), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Canonical | Ubuntu Linux | version 19.04version 12.04version 14.04version 16.04version 18.04version 18.10 | Vulnerable | NIST National Vulnerability Database |
| Debian | Debian Linux | version 8.0version 9.0 | Vulnerable | NIST National Vulnerability Database |
| Fedoraproject | Fedora | version 30version 29 | Vulnerable | NIST National Vulnerability Database |
| Libexpat Project | Libexpat | < 2.2.7 | Vulnerable | NIST National Vulnerability Database |
| Opensuse | Leap | version 15.0version 15.1 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Hospitality Res 3700 | ≥ 5.7 and ≤ 5.7.6 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Http Server | version 12.1.3.0version 12.2.1.4.0 | Vulnerable | NIST National Vulnerability Database |
| Oracle | Outside In Technology | version 8.5.4version 8.5.5 | Vulnerable | NIST National Vulnerability Database |
| Tenable | Nessus | < 8.15.0 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.5 | CVSS 3.1 | High | 3.9 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 7.5 | CVSS 3.1 | High | 3.9 | 3.6 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database |
| 7.5 | CVSS 3.1 | High | — | — | GitHub, Inc. via GitHub Security Advisories |
| 7.5 | CVSS 3.1 | High | — | — | CISA-ADP via CVE Program (cve.org) e CISA ADP |
| 7.8 | CVSS 2.0 | High | 10.0 | 6.9 | nvd@nist.gov via NIST National Vulnerability Database |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 7.11%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Look for parameters with command/query metacharacters and unexpected child processes of the service.
Timeline
What happened to this CVE, newest first.
- 2026
- SSVC assessment updated
- Record published
- Fix documented
- Affected products added · libexpat project/libexpat, canonical/ubuntu linux, debian/debian linux, fedoraproject/fedora, opensuse/leap, oracle/hosp
- CVSS changed · 7.5
- Source status changed · → Modified
- Record created in this database
- 2019
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
31 on the record
- www.oracle.com/security-alerts/cpuoct2020.html
- github.com/libexpat/libexpat/pull/262/commits/11f8838bf99ea0a6f0b76f9760c43704d0
- www.oracle.com/security-alerts/cpuapr2020.html
- www.oracle.com/security-alerts/cpuApr2021.html
- github.com/libexpat/libexpat/pull/262
- github.com/libexpat/libexpat/issues/186
- www.oracle.com/security-alerts/cpuoct2021.html
- nvd.nist.gov/vuln/detail/CVE-2018-20843
- usn.ubuntu.com/4040-2/
- lists.opensuse.org/opensuse-security-announce/2019-07/msg00039.html
- security.netapp.com/advisory/ntap-20190703-0001
- github.com/advisories/GHSA-hj5j-c8qp-mgmv
- seclists.org/bugtraq/2019/Jun/39
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEJJ
- security.gentoo.org/glsa/201911-08
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CEJJ
- www.tenable.com/security/tns-2021-11
- usn.ubuntu.com/4040-1/
- github.com/libexpat/libexpat/blob/R_2_2_7/expat/Changes
- lists.debian.org/debian-lts-announce/2019/06/msg00028.html
- usn.ubuntu.com/4040-1
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IDAU
- support.f5.com/csp/article/K51011533
- usn.ubuntu.com/4040-2
- www.debian.org/security/2019/dsa-4472
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/CEJJSQ
- cert-portal.siemens.com/productcert/html/ssa-398330.html
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IDAU
- bugs.chromium.org/p/oss-fuzz/issues/detail
- security.netapp.com/advisory/ntap-20190703-0001/
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/IDAUGE
Elsewhere on this site
Related CVEs (same products)
- High CVE-2026-103946 SQL Injection 1d
- High CVE-2026-76957 Use After Free in Libexpat Project Libexpat Aug 20, 2026
- High CVE-2026-76956 In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code… Aug 20, 2026
- High CVE-2026-60414 Exposure of Sensitive Information in Oracle Outside In Technology Aug 18, 2026
- High CVE-2026-60412 Deserialization of Untrusted Data in Oracle Outside In Technology Aug 18, 2026
- High CVE-2026-60413 Exposure of Sensitive Information in Oracle Outside In Technology Aug 18, 2026
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2018-20843 is "In libexpat in Expat before 2.2.7, XML input including XML names that contain a large number of...", rated High. It affects Ubuntu Linux (Canonical); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 7.11% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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