libexpat: Inefficient Algorithmic Complexity
CVE-2026-45186 is a high-severity inefficient algorithmic complexity vulnerability in libexpat from Libexpat Project, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 2.8.1 as the first without the flaw, so updating libexpat to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.48% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update libexpat to 2.8.1 or a later version.
- Update SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) to V3.1.6 or a later version.
- Update SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) to V3.1.6 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Libexpat Project | libexpat | before 2.8.1 | 2.8.1 |
| Red Hat | Red Hat Enterprise Linux 10 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 8 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 9 | Not specified in the record | Not stated |
| Red Hat | Red Hat JBoss Core Services 2.4.62.SP4 | Not specified in the record | Not stated |
| Red Hat | Red Hat Discovery 2 | Not specified in the record | Not stated |
| Red Hat | Red Hat Update Infrastructure 5 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 6 | Not specified in the record | Not stated |
| Red Hat | Red Hat Enterprise Linux 7 | Not specified in the record | Not stated |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | V3.1.5 up to, but not including, V3.1.6; V3.1.7 and later | V3.1.6 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | V3.1.5 up to, but not including, V3.1.6; V3.1.7 and later | V3.1.6 |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | V3.1.5 up to, but not including, V3.1.6; V3.1.7 and later | V3.1.6 |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | V3.1.5 up to, but not including, V3.1.6; V3.1.7 and later | V3.1.6 |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | V3.1.5 up to, but not including, V3.1.6; V3.1.7 and later | V3.1.6 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 2.9 | Low | CNA (mitre.org) |
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
In libexpat before 2.8.1, the computational complexity of attribute name collision checks allows a denial of service via moderately sized crafted XML input.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Inefficient Algorithmic Complexity
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
More Inefficient Algorithmic Complexity vulnerabilities (CWE-407)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- github.com/libexpat/libexpat/pull/1216Exploit, Issue Tracking
Third-party and government advisories
- openwall.com/lists/oss-security/2026/05/11/16Mailing List, Third Party Advisory
Other references
- access.redhat.com/errata/RHSA-2026:22715
- access.redhat.com/errata/RHSA-2026:22721
- access.redhat.com/errata/RHSA-2026:23230
- access.redhat.com/errata/RHSA-2026:26319
- access.redhat.com/errata/RHSA-2026:27201
- access.redhat.com/errata/RHSA-2026:29197
- access.redhat.com/errata/RHSA-2026:58981
- access.redhat.com/security/cve/CVE-2026-45186
- bugzilla.redhat.com/show_bug.cgi?id=2468575
- cert-portal.siemens.com/productcert/html/ssa-082556.html
- cert-portal.siemens.com/productcert/html/ssa-457936.html
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-45186.json
Other vulnerabilities in libexpat
- 7.8 High severity
- 7.5 High severity
- 7.5 High severity
- 7.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
Recent Inefficient Algorithmic Complexity vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
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