CVE-2025-52570 — letmeind
Fix: mbuesch/letmein@43207cdCVE-2025-52570 is a CWE-770 vulnerability in letmeind. A fix is available for letmeind — see the affected versions and patch details below.
Letmein connection limiter allows an arbitrary amount of simultaneous connections
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-52570.
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.
Real-World Exposure
letmeind🦀letmeinfwdReal-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
Impact
The connection limiter is implemented incorrectly.
It allows an arbitrary amount of simultaneously incoming connections (TCP, UDP and Unix socket) for the services letmeind and letmeinfwd.
Therefore, the command line option num-connections is not effective and does not limit the number of simultaneously incoming connections.
letmeind is the public network facing daemon (TCP/UDP).
letmeinfwd is the internal firewall daemon that only listens on local Unix socket.
Possible Denial Of Service by resource exhaustion.
Affected versions
All versions <= 10.2.0 are affected.
Patches
All users shall upgrade to version 10.2.1.
Workarounds
Untested possible workarounds:
- It might be possible to limit the number of active connections to the
letmeindport (default 5800) via firewall. - The resource consumption of the service might be restricted with a service manager such as systemd.
Severity:
If a (D)DoS is run against the service, something is going to be affected. The connection limiter assures that the effect on the system itself is limited at the expense of the effect on the letmein services itself. So even with the connection limiter active, a (D)DoS can lead to a less responsive or unresponsive letmein service.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | letmeind | all versions | 10.2.1cargo update -p letmeind --precise 10.2.1 |
| 🦀crates.io | letmeinfwd | all versions | 10.2.1cargo update -p letmeinfwd --precise 10.2.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for letmeind, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update letmeind to 10.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-52570 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-2025-52570 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-52570. 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-2025-52570 in your dependencies?
O3 Security finds CVE-2025-52570 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.