# CVE-2019-11842: matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG

> Attackers can predict authentication tokens or IDs due to poor random number generation, potentially bypassing security or taking over accounts.

- **Severity:** High 7.5 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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:** 9 May 2019
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-gwf7-vfjf-wf6x, PYSEC-2019-185, PYSEC-2026-2620, UBUNTU-CVE-2019-11842

## What is CVE-2019-11842?

CVE-2019-11842 is a high-severity vulnerability in n/a, published on 9 May 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Matrix Sydent before 1.0.3 and Synapse before 0.99.3.1. Random number generation is mishandled, which makes it easier for attackers to predict a Sydent authentication token or a Synapse random ID.

Weakness: CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG))

## Which versions are affected by CVE-2019-11842?

6 open source packages ship an affected version, including matrix-sydent and matrix-synapse. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `matrix-sydent` | PyPI | All versions | 1.0.3 |
| `matrix-sydent` | PyPI | All versions | 1.0.3 |
| `matrix-sydent` | PyPI | All versions | 1.0.3 |
| `matrix-synapse` | PyPI | All versions | 0.99.3.1 |
| `matrix-synapse` | PyPI | All versions | 0.99.3.1 |
| `matrix-synapse` | PyPI | All versions | 0.99.3.1 |

Products: Matrix Sydent, Matrix Synapse.

## How do I fix CVE-2019-11842?

Upgrade matrix-sydent to 1.0.3 or later.

## Is CVE-2019-11842 being exploited?

There is no known exploitation of CVE-2019-11842 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2023-38686](https://insights.sbomify.com/CVE-2023-38686/): Sydent does not verify email server certificates (critical 9.3)
- [CVE-2021-29431](https://insights.sbomify.com/CVE-2021-29431/): SSRF in Sydent due to missing validation of hostnames (high 7.7)
- [CVE-2021-29430](https://insights.sbomify.com/CVE-2021-29430/): Denial of service attack via memory exhaustion (high 7.5)
- [CVE-2019-11340](https://insights.sbomify.com/CVE-2019-11340/): Matrix Sydent mishandles emails (medium 5.9)
- [CVE-2021-29432](https://insights.sbomify.com/CVE-2021-29432/): Malicious users could control the content of invitation emails (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-11842 and fix it if it is affected.

What it is: CVE-2019-11842 is a high-severity vulnerability in n/a, published on 9 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-2019-11842 in the wild and no public exploit code.

Affected packages and fixed versions:
- matrix-sydent (PyPI): affected all versions; fixed in 1.0.3
- matrix-sydent (PyPI): affected all versions; fixed in 1.0.3
- matrix-sydent (PyPI): affected all versions; fixed in 1.0.3
- matrix-synapse (PyPI): affected all versions; fixed in 0.99.3.1
- matrix-synapse (PyPI): affected all versions; fixed in 0.99.3.1
- matrix-synapse (PyPI): affected all versions; fixed in 0.99.3.1

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-2019-11842/ (Markdown: https://insights.sbomify.com/CVE-2019-11842/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-11842
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-11842
- OSV: https://osv.dev/vulnerability/CVE-2019-11842

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-11842/
Summaries are generated and may contain mistakes; the official description above is the record.