# CVE-2019-0820: Regular Expression Denial of Service in System.Text.RegularExpressions

> Attackers can cause a denial of service by submitting specially crafted regular expression strings to applications using .NET Framework or Core.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 May 2019
- **Updated:** 4 Aug 2024
- **Also known as:** ECHO-495f-20f1-b39d, GHSA-cmhx-cq75-c4mj

## What is CVE-2019-0820?

CVE-2019-0820 is a high-severity denial of service vulnerability in Microsoft .Net Framework, published on 16 May 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2019-0820?

2 open source packages ship an affected version, including System.Text.RegularExpressions. It affects 6 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `System.Text.RegularExpressions` | NuGet | From 4.3.0 | 4.3.1 |
| `System.Text.RegularExpressions` | NuGet | From 4.3.0 | 4.3.1 |

Products: Microsoft .Net Core, Microsoft .Net Framework, Redhat Enterprise Linux, Redhat Enterprise Linux Eus, Redhat Enterprise Linux Server Aus, Redhat Enterprise Linux Server Tus.

## How do I fix CVE-2019-0820?

Upgrade System.Text.RegularExpressions to 4.3.1 or later.

## Is CVE-2019-0820 being exploited?

There is no known exploitation of CVE-2019-0820 in the wild and no public exploit code.

## Other vulnerabilities in Microsoft .Net Framework

- [CVE-2020-1147](https://insights.sbomify.com/CVE-2020-1147/): Microsoft .NET Framework, SharePoint, and Visual Studio Remote Code Execution (high 7.8, exploited in the wild)
- [CVE-2020-0605](https://insights.sbomify.com/CVE-2020-0605/): Code injection in .NET Core (high 8.8)
- [CVE-2020-0606](https://insights.sbomify.com/CVE-2020-0606/): Remote code execution in Microsoft.WindowsDesktop.App.Ref (high 8.8)
- [CVE-2019-1301](https://insights.sbomify.com/CVE-2019-1301/): High severity vulnerability that affects System.Management.Automation (high 7.5)
- [CVE-2019-0980](https://insights.sbomify.com/CVE-2019-0980/): Denial of service in ASP.NET Core (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-0820 and fix it if it is affected.

What it is: CVE-2019-0820 is a high-severity denial of service vulnerability in Microsoft .Net Framework, published on 16 May 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-0820 in the wild and no public exploit code.

Affected packages and fixed versions:
- System.Text.RegularExpressions (NuGet): affected from 4.3.0; fixed in 4.3.1
- System.Text.RegularExpressions (NuGet): affected from 4.3.0; fixed in 4.3.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2019-0820/ (Markdown: https://insights.sbomify.com/CVE-2019-0820/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-0820
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-0820
- OSV: https://osv.dev/vulnerability/CVE-2019-0820

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-0820/
Summaries are generated and may contain mistakes; the official description above is the record.