CVE-2024-36403
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 · uneditedMatrix Media Repo (MMR) is a highly configurable multi-homeserver media repository for Matrix. MMR before version 1.3.5 is vulnerable to unbounded disk consumption, where an unauthenticated adversary can induce it to download and cache large amounts of remote media files. MMR's typical operating environment uses S3-like storage as a backend, with file-backed store as an alternative option. Instances using a file-backed store or those which self-host an S3 storage system are therefore vulnerable to a disk fill attack. Once the disk is full, authenticated users will be unable to upload new media, resulting in denial of service. For instances configured to use a cloud-based S3 storage option, this could result in high service fees instead of a denial of service. MMR 1.3.5 introduces a new default-on "leaky bucket" rate limit 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. Operators should note that the leaky bucket implementation introduced in MMR 1.3.5 requires the IP address associated with the request to be forwarded, to avoid mistakenly applying the rate limit to the reverse proxy instead. To avoid this issue, the reverse proxy should populate the X-Forwarded-For header when sending the request to MMR. Operators who cannot update may wish to lower the maximum file size they allow and implement harsh rate limits, though this can still lead to a large amount of data to be downloaded.
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 confidenceMatrix Media Repo before v1.3.5 lacks rate limiting on remote media caching, allowing unauthenticated attackers to trigger unbounded downloads that fill disk storage or rack up S3 storage fees. The vulnerability stems from no per-user or per-IP limits on how much remote content MMR will fetch and cache locally.
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< 1.3.5CVSS 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
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Check MMR installed versionRun 'mmr --version' or check the Docker image tag/git tag used for deploymentAffected if Version is below 1.3.5
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Verify remote media caching is enabledInspect MMR configuration file (typically config.yaml) for 'remote_media' or 'download' settings that enable fetching and caching of remote contentAffected if Remote media caching is enabled and version is vulnerable
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Confirm no per-user or per-IP rate limits existReview configuration for 'rate_limit' or 'leaky_bucket' settings under remote media sectionsAffected if No rate limiting is configured for remote media downloads
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Check if X-Forwarded-For headers are forwardedReview reverse proxy (nginx/apache) configuration for 'proxy_set_header X-Forwarded-For' or equivalent directiveAffected if Proxy does not forward client IPs, making rate limiting less effective even if enabled
A user is affected if they run MMR version below 1.3.5 with remote media caching enabled and without configured rate limits on remote content downloads.
Generated from the published advisory. Verify against your own configuration.
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 · scoped1.3.5
Upgrade to MMR 1.3.5+ to enable the leaky bucket rate limit, and configure the reverse proxy to forward X-Forwarded-For headers so the rate limit applies to client IPs rather than the proxy itself. As additional hardening, lower maximum allowed file sizes and implement aggressive rate limits at the proxy level.
1.3.5
- Upgrade Matrix Media Repo to version 1.3.5 or later to obtain the leaky bucket rate limit protection
- Configure the reverse proxy to populate the X-Forwarded-For header when forwarding requests to MMR, to ensure the rate limit applies to the client IP rather than the proxy IP
- Verify the leaky bucket rate limit is functioning (it is enabled by default in 1.3.5)
- For additional hardening, consider lowering maximum file size limits and implementing stricter rate limits at the reverse proxy level
Generated from the published advisory — verify against the referenced sources before acting.
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- Implementation2.0 h
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- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2024-36403 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2024-36403 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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