CVE-2021-23840

HIGHNVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 33% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Elevated
7.5
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 51%
CISA-KEV: Not listedEPSS: 51%CVSS: 7.5Exploit: NoneExposed: 0

A fix is available — apply it.

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).

CVSS v3
7.5
EG Score
7.5(medium)
EPSS
98.8%
KEV
Not listed

Published

February 16, 2021

Last Modified

April 16, 2026

References (40)

Vendor Advisories for CVE-2021-23840(4)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(10)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuopenssl (1.0.2g-1ubuntu4.19) @ xenial2026-05-22ubuntu
ubuntuopenssl (1.0.1f-1ubuntu2.27+esm10) @ trusty2026-05-22ubuntu
ubuntuovmf (2020.11-4ubuntu0.1) @ hirsute2026-05-22ubuntu
redhatpatch2021-11-30redhat
redhatjws5-tomcat-vault-0:1.1.8-4.Final_redhat_00004.1.el8jws2021-11-30redhat
redhatopenssl2021-11-10redhat
redhatjbcs-httpd24-openssl-pkcs11-0:0.4.10-22.jbcs.el72021-11-10redhat
redhatopenssl-1:1.1.1k-4.el82021-11-09redhat
redhatedk2-0:20210527gite1999b264f1f-3.el82021-11-09redhat
redhatopenssl-1:1.0.2k-22.el7_92021-10-12redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
crates.io(1)
PackageVulnerable rangeFixed inDependents
openssl-src—111.14.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(8)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 4× in last 7d / 30× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 109 total refreshes for this CVE.

  1. 2026-07-11 13:22 UTCOSV refresh
  2. 2026-07-11 08:25 UTCEPSS rescore
  3. 2026-07-09 19:07 UTCEPSS rescore
  4. 2026-07-08 15:12 UTCEPSS rescore
  5. 2026-07-04 06:29 UTCEPSS rescore
  6. 2026-07-04 06:29 UTCEPSS rescore
  7. 2026-07-02 16:57 UTCEPSS rescore
  8. 2026-07-01 15:03 UTCEPSS rescore
  9. 2026-06-28 04:54 UTCEPSS rescore
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  11. 2026-06-27 03:06 UTCEPSS rescore
  12. 2026-06-27 03:06 UTCEPSS rescore
  13. 2026-06-25 13:48 UTCEPSS rescore
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  15. 2026-06-24 14:03 UTCEPSS rescore
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  17. 2026-06-23 21:31 UTCEPSS rescore
  18. 2026-06-23 21:31 UTCEPSS rescore
  19. 2026-06-22 19:35 UTCOSV refresh
  20. 2026-06-21 01:58 UTCEPSS rescore
  21. 2026-06-21 01:57 UTCEPSS rescore
  22. 2026-06-18 17:51 UTCEPSS rescore
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  24. 2026-06-17 17:51 UTCEPSS rescore
  25. 2026-06-16 17:50 UTCEPSS rescore
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  1. 2026-06-15 17:46 UTCEPSS rescore
  2. 2026-06-14 23:15 UTCEPSS rescore
  3. 2026-06-13 22:58 UTCEPSS rescore
  4. 2026-06-12 23:10 UTCEPSS rescore
  5. 2026-06-12 23:10 UTCEPSS rescore
  6. 2026-06-11 13:58 UTCEPSS rescore
  7. 2026-06-10 22:16 UTCEPSS rescore
  8. 2026-06-10 22:16 UTCEPSS rescore
  9. 2026-06-10 13:20 UTCEPSS rescore
  10. 2026-06-08 14:15 UTCEPSS rescore
  11. 2026-06-08 14:15 UTCEPSS rescore
  12. 2026-06-07 15:23 UTCEPSS rescore
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  14. 2026-06-06 13:46 UTCEPSS rescore
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  17. 2026-06-05 22:45 UTCEPSS rescore
  18. 2026-06-05 22:45 UTCEPSS rescore
  19. 2026-06-05 10:00 UTCOSV refresh
  20. 2026-06-05 06:09 UTCEPSS rescore
  21. 2026-06-05 06:09 UTCEPSS rescore
  22. 2026-06-05 06:08 UTCEPSS rescore
  23. 2026-06-04 13:10 UTCEPSS rescore
  24. 2026-06-02 20:11 UTCEPSS rescore
  25. 2026-06-02 20:11 UTCEPSS rescore
  26. 2026-06-01 13:50 UTCEPSS rescore
  27. 2026-06-01 13:50 UTCEPSS rescore
  28. 2026-05-31 22:29 UTCEPSS rescore
  29. 2026-05-31 22:29 UTCEPSS rescore
  30. 2026-05-31 00:15 UTCEPSS rescore
  31. 2026-05-31 00:15 UTCEPSS rescore
  32. 2026-05-29 13:42 UTCEPSS rescore
  33. 2026-05-28 13:43 UTCEPSS rescore
  34. 2026-05-28 13:43 UTCEPSS rescore
  35. 2026-05-27 13:39 UTCEPSS rescore
  36. 2026-05-26 13:42 UTCEPSS rescore
  37. 2026-05-26 13:42 UTCEPSS rescore
  38. 2026-05-26 07:17 UTCEPSS rescore
  39. 2026-05-26 07:17 UTCEPSS rescore
  40. 2026-05-24 16:49 UTCEPSS rescore
  41. 2026-05-23 00:10 UTCEG score recompute
  42. 2026-05-22 21:16 UTCEPSS rescore
  43. 2026-05-22 21:16 UTCEPSS rescore
  44. 2026-05-22 21:16 UTCEPSS rescore
  45. 2026-05-22 21:16 UTCEPSS rescore
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  49. 2026-05-22 21:16 UTCEPSS rescore
  50. 2026-05-22 21:16 UTCEPSS rescore
  51. 2026-05-22 06:48 UTCEG score recompute
  52. 2026-05-22 06:48 UTCVendor advisory
  53. 2026-05-21 22:41 UTCEPSS rescore
  54. 2026-05-21 22:41 UTCEPSS rescore
  55. 2026-05-21 22:41 UTCEPSS rescore
  56. 2026-05-20 22:37 UTCEPSS rescore
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  67. 2026-05-20 11:21 UTCEPSS rescore
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  75. 2026-05-20 11:21 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-23840?
CVE-2021-23840 is a high vulnerability published on February 16, 2021. Calls to EVPCipherUpdate, EVPEncryptUpdate 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…
When was CVE-2021-23840 disclosed?
CVE-2021-23840 was first published in the National Vulnerability Database on February 16, 2021, with the most recent update on April 16, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-23840 actively exploited?
CVE-2021-23840 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 98.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-23840?
CVE-2021-23840 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2021-23840?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-23840, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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