CVE-2021-23840
HIGHEPSS 99th pctlDescription
Calls to EVP_CipherUpdate, EVP_EncryptUpdate and EVP_DecryptUpdate may overflow the output length argument in some cases where the input length is close to the maximum permissable length for an integer on the platform. In such cases the return value from the function call will be 1 (indicating success), but the output length value will be negative. This could cause applications to behave incorrectly or crash. OpenSSL versions 1.1.1i and below are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1j. OpenSSL versions 1.0.2x and below are affected by this issue. However OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i). Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x).
How to fix
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.
This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2023-05-31. Extended security maintenance is available until 2028-04-01.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
This Ubuntu release reached end-of-life on 2025-05-31. Extended security maintenance is available until 2030-04-02.
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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:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Very high risk: more likely to be exploited than 99% of all known CVEs.
References
Related Vulnerabilities
Other CWE-190 (Integer Overflow) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2020-16040 | Medium | 6.5 | 100% | - | Fix |
| CVE-2019-11477 | High | 7.5 | 99% | - | Fix |
| CVE-2023-44443 | High | 7.8 | 94% | - | Fix |
| CVE-2014-0569 | High | 9.3 | 91% | - | - |
| CVE-2017-3599 | High | 7.5 | 90% | - | Fix |
| CVE-2023-21716 | Critical | 9.8 | 82% | - | Fix |
Common questions
How do I fix CVE-2021-23840?
Published advisories record a fix for 29 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-2021-23840 being actively exploited?
Not that we know of. CVE-2021-23840 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 50.7% is the estimated probability that it will be exploited in the next 30 days. That is higher than 99% of all scored CVEs.
How severe is CVE-2021-23840?
CVE-2021-23840 has a CVSS v3 base score of 7.5, rated high. 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-2021-23840 affect?
Published advisories record a fix for edk2-aarch64 (Amazon), edk2-debuginfo (Amazon), edk2-ovmf (Amazon), edk2-tools (Amazon), and 25 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.