# CVE-2020-26890: Denial of service attack due to invalid JSON

Source: https://junglewise.ai/threats/cve-2020-26890-denial-of-service-attack-due-to-invalid-json  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2020-11-24  
License: CC BY 4.0 with a link back

CVE-2020-26890 · Severity: low · CVSS 3.1 · Published 2020-11-24

Matrix Synapse before 1.20.0 erroneously permits non-standard NaN, Infinity, and -Infinity JSON values in fields of m.room.member events, allowing remote attackers to execute a denial of service attack against the federation and common Matrix clients. If such a malformed event is accepted into the room's state, the impact is long-lasting and is not fixed by an upgrade to a newer version, requiring the event to be manually redacted instead. Since events are replicated to servers of other room members, the impact is not constrained to the server of the event sender.

Technologies: [matrix-synapse (PyPI)](https://junglewise.ai/threats/technologies/matrix-synapse). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2020-26890 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2020-26890 being exploited in the wild.

**How severe is CVE-2020-26890?** Low severity, with a CVSS score of 3.1, published 24 November 2020.

**Which products and versions are affected?** matrix-synapse (PyPI) ECOSYSTEM:introduced=0,fixed=1.20.0.

**Is there a fix for CVE-2020-26890?** Yes. matrix-synapse (PyPI): upgrade to 1.20.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2020-26890?** Check whether you run matrix-synapse (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- matrix-synapse (PyPI): upgrade to 1.20.0 or later

  ```sh
  pip install "matrix-synapse>=1.20.0"
  ```


## Affected products

- matrix-synapse (PyPI) ECOSYSTEM:introduced=0,fixed=1.20.0

## Identifiers

- CVE-2020-26890
- GHSA-4mp3-385r-v63f
- PYSEC-2020-237

## Related threats

- [PYSEC-2026-2620 - matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG](https://junglewise.ai/threats/cve-2019-11842-matrix-sydent-and-matrix-synapse-use-cryptographically-weak-prng)
- [PYSEC-2026-1614 - Synapse vulnerable to federation denial of service via malformed events](https://junglewise.ai/threats/cve-2025-30355-synapse-vulnerable-to-federation-denial-of-service-via-malformed)
- [PYSEC-2026-1610 - Synapse Matrix has a partial room state leak via Sliding Sync](https://junglewise.ai/threats/cve-2024-53867-synapse-matrix-has-a-partial-room-state-leak-via-sliding-sync)
- [Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders](https://junglewise.ai/threats/cve-2024-53863-synapse-can-be-forced-to-thumbnail-unexpected-file-formats)
- [PYSEC-2026-1611 - Synapse allows a a malformed invite to break the invitee's `/sync`](https://junglewise.ai/threats/cve-2024-52815-synapse-allows-a-a-malformed-invite-to-break-the-invitee-s-sync)