CVE-2021-23841 — openssl-src
MEDIUMCVE-2021-23841 is a medium-severity (CVSS 5.9) NULL Pointer Dereference vulnerability in openssl-src. A fix is available for openssl-src — see the affected versions and patch details below.
Integer Overflow in openssl-src
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-23841.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-23841 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
openssl-srcReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
The OpenSSL public API function X509_issuer_and_serial_hash() attempts to create a unique hash value based on the issuer and serial number data contained within an X509 certificate. However it fails to correctly handle any errors that may occur while parsing the issuer field (which might occur if the issuer field is maliciously constructed). This may subsequently result in a NULL pointer deref and a crash leading to a potential denial of service attack. The function X509_issuer_and_serial_hash() is never directly called by OpenSSL itself so applications are only vulnerable if they use this function directly and they use it on certificates that may have been obtained from untrusted sources. 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).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | openssl-src | all versions | 111.14.0cargo update -p openssl-src --precise 111.14.0 |
Affected Products
ipadosappleiphone osapplemacosapplesafariappledebian linuxdebianoncommand insightnetappDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for openssl-src, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update openssl-src to 111.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23841 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is a a null pointer dereference in the X509_issuer_and_serial_hash() function, which can result in crash if called by an application compiled with OpenSSL, by passing a specially-crafted certificate. OpenSSL internally does not use this function.
As per upstream "The function X509_issuer_and_serial_hash() is never directly called by OpenSSL itself so applications are only vulnerable if they use this function directly and they use it on certificates that may have been obtained from untrusted sources."Source: Red Hat security advisory for CVE-2021-23841 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| JBoss Core Services for RHEL 8 | jbcs-httpd24-apr-0:1.6.3-107.el8jbcs | RHSA-2021:4614 |
| Red Hat Enterprise Linux 7 | openssl-1:1.0.2k-22.el7_9 | RHSA-2021:3798 |
| Red Hat Enterprise Linux 8 | edk2-0:20210527gite1999b264f1f-3.el8 | RHSA-2021:4198 |
| Red Hat Enterprise Linux 8 | openssl-1:1.1.1k-4.el8 | RHSA-2021:4424 |
| Red Hat JBoss Core Services | jbcs-httpd24-openssl | RHSA-2021:4613 |
| Red Hat JBoss Web Server 5 | see advisory | RHSA-2021:4863 |
| Red Hat JBoss Web Server 5.6 on RHEL 7 | jws5-tomcat-0:9.0.50-3.redhat_00004.1.el7jws | RHSA-2021:4861 |
Frequently Asked Questions
Is CVE-2021-23841 in your dependencies?
Find it across crates.io, including transitive dependencies.