Letmein connection limiter allows an arbitrary amount of simultaneous connections

published 2025-06-23 16 mo ago modified 2026-06-17 4 mo ago also GHSA-jpv7-p47h-f43j , EUVD-2025-19032

cvss: 1.7; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 31%
public exploits: 0; none known

Letmein is an authenticating port knocker. Prior to version 10.2.1, 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. This issue has been patched in version 10.2.1.

Patch / fix

fixed in 2 links 1

crates.io letmeind 10.2.1
crates.io letmeinfwd 10.2.1

github.com/mbuesch/letmein@43207cd commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 16 mo ago (2025-06-24)

Exploit prediction

0.38% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	1.7	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U
CNA	4.0	1.7	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected packages

ecosystem	package	affected	fixed in
crates.io	letmeind	<10.2.1	10.2.1
crates.io	letmeinfwd	<10.2.1	10.2.1

Affected products

mbuesch letmein

Classification

Weakness

CWE-799 Improper Control of Interaction Frequency
CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary