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SynapseApplication · Matrix

CVE-2024-37302

HIGH · 7.5 CVSS v3.1 Published 2024-12-03
Fix available
A fix is available. Upgrade to 1.106.0 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Synapse is an open-source Matrix homeserver. Synapse versions before 1.106 are vulnerable to a disk fill attack, where an unauthenticated adversary can induce Synapse to download and cache large amounts of remote media. The default rate limit strategy is insufficient to mitigate this. This can lead to a denial of service, ranging from further media uploads/downloads failing to completely unavailability of the Synapse process, depending on how Synapse was deployed. Synapse 1.106 introduces a new "leaky bucket" rate limit on remote media downloads to reduce the amount of data a user can request at a time. This does not fully address the issue, but does limit an unauthenticated user's ability to request large amounts of data to be cached.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Synapse Matrix homeserver versions before 1.106 are vulnerable to a disk fill attack where unauthenticated adversaries can induce the server to download and cache arbitrarily large amounts of remote media, overwhelming storage and causing denial of service. The default rate limiting is insufficient to prevent this abuse. Version 1.106 introduces a leaky bucket rate limit on remote media downloads to restrict how much data can be cached, though this is acknowledged as an incomplete fix.

MitigationUpgrade to Synapse 1.106 or later and configure the new leaky bucket rate limiting for remote media. Given that the official fix is acknowledged as incomplete, consider additional hardening such as media storage isolation, aggressive caching policies, and monitoring for anomalous download patterns.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
SynapseApplication
Affected:< 1.106.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Synapse version
    Run `python -c "import synapse; print(synapse.__version__)"` or check your package manager for the installed synapse package version
    Affected if The installed version is below 1.106.0
  2. Check if remote media caching is enabled
    Inspect your homeserver.yaml configuration file and look for settings that enable fetching of remote media from other Matrix servers (such as settings related to media retention, remote media downloading, or thumbnail generation from non-local URLs)
    Affected if Remote media fetching from other Matrix servers is enabled and caching is permitted
  3. Verify rate limiting on remote media downloads
    Examine your homeserver.yaml for rate limiting configurations related to remote media downloads. In versions before 1.106, the default settings allow unlimited remote media caching
    Affected if No leaky bucket rate limit or insufficient rate limiting is configured for remote media downloads; the server relies on default rate limits only
  4. Check media storage configuration
    Review your media store paths and any retention policies in homeserver.yaml. Look for settings controlling how long remote media is cached and maximum storage limits
    Affected if Remote media is stored without aggressive retention limits or storage quotas, allowing unbounded cache growth

You are affected if your Synapse version is below 1.106.0 AND remote media fetching from other Matrix servers is enabled without proper rate limiting on downloads.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 1.106.0 or later
Fixed in 1.106.0
Interim mitigation

Upgrade to Synapse 1.106 or later and configure the new leaky bucket rate limiting for remote media. Given that the official fix is acknowledged as incomplete, consider additional hardening such as media storage isolation, aggressive caching policies, and monitoring for anomalous download patterns.

Recommended fix High confidence

1.106.0

  1. Check current Synapse version using 'pip show synapse' or your package manager
  2. Consult the official Synapse upgrade documentation at https://matrix-org.github.io/synapse/latest/upgrade.html
  3. Create a full backup of your Synapse database and configuration files
  4. Stop the Synapse service
  5. Upgrade Synapse using your package manager (e.g., 'pip install --upgrade synapse' or your system package manager)
  6. Verify the installed version is 1.106.0 or later using 'pip show synapse'
  7. Restart the Synapse service
  8. Monitor logs for any errors or issues following the upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Synapse Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,780
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2024-37302 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data