Is CVE-2021-23840 in the CISA KEV catalog?

No. CVE-2021-23840 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-23840?

CVE-2021-23840 has a CVSS v3 base score of 7.5 (HIGH).

What is the EPSS score for CVE-2021-23840?

CVE-2021-23840 has an EPSS score of 50.73% (99th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-23840?

Upgrade openssl on debian 11 to 1.1.1j-1 or later. Fixes are available for 12 affected products.

CVE & CISA-KEV Catalog

CVE-2021-23840

HIGHEPSS 99th pctl

7.5

CVSS v3

NVD

Description

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).

CWE-190Integer Overflow

How to fix

Remediation Available

opensslDebian

Fixed in:1.1.1j-1CVE-2021-23840

edk2Ubuntu

Fixed in:0~20191122.bd85bf54-2ubuntu3.3USN-5088-1

libssl1.0.0Ubuntu

Fixed in:1.0.1f-1ubuntu2.27+esm10USN-7018-1

Fixed in:1.0.2g-1ubuntu4.19USN-4738-1

Fixed in:1.0.2n-1ubuntu5.6USN-4738-1

libssl1.1Ubuntu

Fixed in:1.1.1-1ubuntu2.1~18.04.8USN-4738-1

Fixed in:1.1.1f-1ubuntu2.2USN-4738-1

opensslUbuntu

Fixed in:1.0.1f-1ubuntu2.27+esm10USN-7018-1

Fixed in:1.0.2g-1ubuntu4.19USN-4738-1

Fixed in:1.1.1-1ubuntu2.1~18.04.8USN-4738-1

Fixed in:1.1.1f-1ubuntu2.2USN-4738-1

openssl1.0Ubuntu

Fixed in:1.0.2n-1ubuntu5.6USN-4738-1

ovmfUbuntu

Fixed in:0~20191122.bd85bf54-2ubuntu3.3USN-5088-1

qemu-efiUbuntu

Fixed in:0~20191122.bd85bf54-2ubuntu3.3USN-5088-1

qemu-efi-aarch64Ubuntu

Fixed in:0~20191122.bd85bf54-2ubuntu3.3USN-5088-1

qemu-efi-armUbuntu

Fixed in:0~20191122.bd85bf54-2ubuntu3.3USN-5088-1

Node.jsWindows application

Affected:12.13.0 12.21.0Fixed in:12.21.0Node.js Foundation

Affected:10.13.0 10.24.0Fixed in:10.24.0Node.js Foundation

Affected:15.0.0 15.10.0Fixed in:15.10.0Node.js Foundation

Node.js (LTS)Windows application

Affected:15.0.0 15.10.0Fixed in:15.10.0Node.js Foundation

Affected:10.13.0 10.24.0Fixed in:10.24.0Node.js Foundation

Affected:12.13.0 12.21.0Fixed in:12.21.0Node.js Foundation

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

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

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploit Intelligence

50.73%probability of exploitation in 30 days

99thpercentile

Very high risk: more likely to be exploited than 99% of all known CVEs.

References

Patch5

Vendor Advisory1

openssl.org

Third-Party Advisory9

Other references5

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	90%	-	-
CVE-2017-3599	High	7.5	90%	-	Fix
CVE-2023-21716	Critical	9.8	82%	-	Fix

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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 2026-04-16.