CVE-2021-23840

HIGH

OpenSSL 1.0.2-1.0.2x and 1.1.1-1.1.1i - Integer Overflow in EVP_CipherUpdate

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 1 public exploit for CVE-2021-23840. PoCs published by Trinadh465.

AI-analyzed exploit summary This repository contains configuration files and documentation related to OpenSSL 1.1.1g, specifically focusing on CVE-2021-23840. It includes detailed explanations of build configurations, target platforms, and helper scripts but lacks functional exploit code.

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).

Exploits (1)

nomisec WRITEUP
by Trinadh465 · poc
https://github.com/Trinadh465/openssl-1.1.1g_CVE-2021-23840

This repository contains configuration files and documentation related to OpenSSL 1.1.1g, specifically focusing on CVE-2021-23840. It includes detailed explanations of build configurations, target platforms, and helper scripts but lacks functional exploit code.

Classification
Writeup 90%
Attack Type
Other
Complexity
Moderate
Reliability
Theoretical
Target: OpenSSL 1.1.1g
No auth needed
Prerequisites: Understanding of OpenSSL build configurations
devstral-2 · analyzed Feb 18, 2026 Full analysis →

References (20)

Core 20
Core References
Third Party Advisory vendor-advisory
https://www.debian.org/security/2021/dsa-4855
Third Party Advisory vendor-advisory
https://security.gentoo.org/glsa/202103-03

Scores

CVSS v3 7.5
EPSS 0.0054
EPSS Percentile 68.2%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CISA SSVC

Vulnrichment
Exploitation none
Automatable yes
Technical Impact partial

Details

CWE
CWE-190
Status published
Products (36)
crates.io/openssl-src 0 - 111.14.0crates.io
debian/debian_linux 10.0
fujitsu/m10-1_firmware < xcp2410
fujitsu/m10-4_firmware < xcp2410
fujitsu/m10-4s_firmware < xcp2410
fujitsu/m12-1_firmware < xcp2410
fujitsu/m12-2_firmware < xcp2410
fujitsu/m12-2s_firmware < xcp2410
mcafee/epolicy_orchestrator 5.10.0 (11 CPE variants)
mcafee/epolicy_orchestrator < 5.10.0
... and 26 more
Published Feb 16, 2021
Tracked Since Feb 18, 2026