CVE-2019-0820 — System.Text.RegularExpres…
HIGHCVE-2019-0820 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in System.Text.RegularExpressions. A fix is available for System.Text.RegularExpressions — see the affected versions and patch details below.
Regular Expression Denial of Service in System.Text.RegularExpressions
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2019-0820 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
System.Text.RegularExpressionsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
A denial of service vulnerability exists when .NET Framework and .NET Core improperly process RegEx strings, aka '.NET Framework and .NET Core Denial of Service Vulnerability'. This CVE ID is unique from CVE-2019-0980, CVE-2019-0981.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | System.Text.RegularExpressions | ≥ 4.3.0&&< 4.3.1 | 4.3.1dotnet add package System.Text.RegularExpressions --version 4.3.1 |
Affected Products
.net coremicrosoft.net frameworkmicrosoftenterprise linuxredhatenterprise linux eusredhatenterprise linux server ausredhatenterprise linux server tusredhatDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for System.Text.RegularExpressions, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update System.Text.RegularExpressions to 4.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-0820 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| .NET Core on Red Hat Enterprise Linux | rh-dotnet21-0:2.1-10.el7 | RHSA-2019:1236 |
| Red Hat Enterprise Linux 8 | dotnet-0:2.1.507-2.el8_0 | RHSA-2019:1259 |
Frequently Asked Questions
Is CVE-2019-0820 in your dependencies?
Find it across NuGet, including transitive dependencies.