CVE-2025-52570Network attack vector

Denial of service via prematurely released permits

Published Jun 24, 2025 · Updated Jun 24, 2025

Resource exhaustion in Michael Büsch letmein before 10.2.1 allows remote attackers to interrupt service through concurrent connections. In letmeind and letmeinfwd, each acquired semaphore permit is dropped before its spawned connection task finishes, so num-connections never constrains active handlers. Unauthenticated TCP or UDP access to letmeind is sufficient; holding many connections open consumes resources and degrades service or host responsiveness.

CVSS severityUnavailable
Unscored
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Michael Büsch letmein before 10.2.1 allows remote attackers to interrupt service through concurrent connections. In letmeind and letmeinfwd, each acquired semaphore permit is dropped before its spawned connection task finishes, so num-connections never constrains active handlers. Unauthenticated TCP or UDP access to letmeind is sufficient; holding many connections open consumes resources and degrades service or host responsiveness.

The record

CVE
CVE-2025-52570
Published
Jun 24, 2025
Updated
Jun 24, 2025
Vendor
Michael Büsch
Product
letmein
Classifications
CWE-799, CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 24, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 24, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 10.2.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Michael Büsch · letmeinversion=< 10.2.1

Published CVSS scores

1.7GitHub, Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-799Improper Control of Interaction Frequency
CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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