CVE-2024-23649 is a high-severity (CVSS 7.5) Information Exposure vulnerability in lemmy_server. A fix is available for lemmy_server — see the affected versions and patch details below.
Any authenticated user may obtain private message details from other users on the same instance
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2024-23649 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,238 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
lemmy_serverReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Lemmy is a link aggregator and forum for the fediverse. Starting in version 0.17.0 and prior to version 0.19.1, users can report private messages, even when they're neither sender nor recipient of the message. The API response to creating a private message report contains the private message itself, which means any user can just iterate over message ids to (loudly) obtain all private messages of an instance. A user with instance admin privileges can also abuse this if the private message is removed from the response, as they're able to see the resulting reports.
Creating a private message report by POSTing to /api/v3/private_message/report does not validate whether the reporter is the recipient of the message. lemmy-ui does not allow the sender to report the message; the API method should likely be restricted to accessible to recipients only. The API response when creating a report contains the private_message_report_view with all the details of the report, including the private message that has been reported:
Any authenticated user can obtain arbitrary (untargeted) private message contents. Privileges required depend on the instance configuration; when registrations are enabled without application system, the privileges required are practically none. When registration applications are required, privileges required could be considered low, but this assessment heavily varies by instance.
Version 0.19.1 contains a patch for this issue. A workaround is available. If an update to a fixed Lemmy version is not immediately possible, the API route can be blocked in the reverse proxy. This will prevent anyone from reporting private messages, but it will also prevent exploitation before the update has been applied.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | lemmy_server | ≥ 0.17.0&&< 0.19.1 | 0.19.1cargo update -p lemmy_server --precise 0.19.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for lemmy_server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update lemmy_server to 0.19.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-23649 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2024-23649 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-23649. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2024-23649 in your dependencies?
O3 Security finds CVE-2024-23649 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.