CVE-2025-43857
MEDIUMDescription
Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5, there is a possibility for denial of service by memory exhaustion when net-imap reads server responses. At any time while the client is connected, a malicious server can send can send a "literal" byte count, which is automatically read by the client's receiver thread. The response reader immediately allocates memory for the number of bytes indicated by the server response. This should not be an issue when securely connecting to trusted IMAP servers that are well-behaved. It can affect insecure connections and buggy, untrusted, or compromised servers (for example, connecting to a user supplied hostname). This issue has been patched in versions 0.5.7, 0.4.20, 0.3.9, and 0.2.5.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Exploit Intelligence
Low risk: more likely to be exploited than 39% of all known CVEs.
References
Related Vulnerabilities
Other CWE-400 (Resource Exhaustion) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2023-44487 | High | 7.5 | 100% | KEV | Fix |
| CVE-2021-44228 | Critical | 10.0 | 100% | KEV + Ransom | Fix |
| CVE-2011-3192 | High | 7.8 | 99% | - | Fix |
| CVE-2019-11478 | Medium | 5.3 | 95% | - | Fix |
| CVE-2023-21547 | High | 7.5 | 89% | - | Fix |
| CVE-2018-1000115 | High | 7.5 | 88% | - | Fix |
Common questions
How do I fix CVE-2025-43857?
Published advisories record a fix for 32 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2025-43857 being actively exploited?
Not that we know of. CVE-2025-43857 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.47% is the estimated probability that it will be exploited in the next 30 days. That is higher than 39% of all scored CVEs.
How severe is CVE-2025-43857?
CVE-2025-43857 has a CVSS v3 base score of 6.5, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2025-43857 affect?
Published advisories record a fix for ruby3.2 (Amazon), ruby3.2-bundled-gems (Amazon), ruby3.2-bundled-gems-debuginfo (Amazon), ruby3.2-debuginfo (Amazon), and 28 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.