Continuous ACME retries via backoff timer overflow
Published Dec 5, 2025 · Updated Dec 5, 2025
Integer overflow in mod_md in Apache HTTP Server 2.4.30 through 2.4.65 allows attackers to trigger continuous ACME renewal retries. The module doubles its retry delay after consecutive renewal errors until integer arithmetic overflows and collapses the backoff timer to zero. Automatic mod_md renewal and sustained failures are required; default settings reach the condition after about 30 days, causing uninterrupted retries until renewal succeeds.
Summary
What happened
Integer overflow in mod_md in Apache HTTP Server 2.4.30 through 2.4.65 allows attackers to trigger continuous ACME renewal retries. The module doubles its retry delay after consecutive renewal errors until integer arithmetic overflows and collapses the backoff timer to zero. Automatic mod_md renewal and sustained failures are required; default settings reach the condition after about 30 days, causing uninterrupted retries until renewal succeeds.
The record
- CVE
- CVE-2025-55753
- Published
- Dec 5, 2025
- Updated
- Dec 5, 2025
- Vendor
- The Apache Software Foundation
- Product
- Apache HTTP Server
- Classifications
- CWE-190
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Dec 5, 2025CVE publishedPublication date reported by the CVE source.
- Dec 5, 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?
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- Affected versionversion=2.4.30 <2.4.66
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What is affected?
Published CVSS scores
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Attacks
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Technologies
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