# CVE-2020-28042: Signature validation bypass in ServiceStack

> Attackers can bypass JWT signature verification in ServiceStack, potentially gaining unauthorized access to protected resources.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Nov 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-v5rv-hpxg-8x49

## What is CVE-2020-28042?

CVE-2020-28042 is a medium-severity authentication bypass vulnerability in n/a, published on 1 Nov 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

ServiceStack before 5.9.2 mishandles JWT signature verification unless an application has a custom ValidateToken function that establishes a valid minimum length for a signature.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2020-28042?

2 open source packages ship an affected version, including ServiceStack. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ServiceStack` | NuGet | All versions | 5.9.2 |
| `ServiceStack` | NuGet | All versions | 5.9.2 |

Products: Servicestack Servicestack.

## How do I fix CVE-2020-28042?

Upgrade ServiceStack to 5.9.2 or later.

## Is CVE-2020-28042 being exploited?

There is no known exploitation of CVE-2020-28042 in the wild and no public exploit code.

Public exploit code:

- 针对JWT渗透开发的漏洞验证/密钥爆破工具，针对CVE-2015-9235/空白密钥/未验证签名攻击/CVE-2016-10555/CVE-2018-0114/CVE-2020-28042的结果生成用于FUZZ，也可使用字典/字符枚举(包括JJWT)的方式进行爆破(JWT Crack) (github_poc): https://github.com/z-bool/Venom-JWT

## Other vulnerabilities in n/a

- [CVE-2025-6445](https://insights.sbomify.com/CVE-2025-6445/): ServiceStack FindType Directory Traversal Remote Code Execution Vulnerability (high 8.1)
- [CVE-2019-1010199](https://insights.sbomify.com/CVE-2019-1010199/): Cross site scripting attack in ServiceStack Framework (medium 6.1)
- [CVE-2025-6444](https://insights.sbomify.com/CVE-2025-6444/): ServiceStack GetErrorResponse Improper Input Validation NTLM Relay Vulnerability (medium 5.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-28042 and fix it if it is affected.

What it is: CVE-2020-28042 is a medium-severity authentication bypass vulnerability in n/a, published on 1 Nov 2020. 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-2020-28042 in the wild and no public exploit code.

Affected packages and fixed versions:
- ServiceStack (NuGet): affected all versions; fixed in 5.9.2
- ServiceStack (NuGet): affected all versions; fixed in 5.9.2

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-2020-28042/ (Markdown: https://insights.sbomify.com/CVE-2020-28042/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-28042
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-28042
- OSV: https://osv.dev/vulnerability/CVE-2020-28042

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-28042/
Summaries are generated and may contain mistakes; the official description above is the record.