CVE-2026-34180 is a high-severity (CVSS 7.5) Out-of-bounds Read vulnerability. A fix is available — see the affected versions and patch details below.
Heap Buffer Over-read in ASN.1 Content Parsing
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-2026-34180.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-34180 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
Issue summary: Parsing a crafted DER-encoded ASN.1 structure with a primitive element whose content exceeds 2 gigabytes in length may cause a heap buffer over-read on 64-bit Unix and Unix-like platforms.
Impact summary: The heap buffer over-read may crash the application (Denial of Service) or to load into the decoded ASN.1 object contents of memory beyond the end of the input buffer. More typically such ASN.1 elements would instead be truncated.
An integer truncation in OpenSSL's ASN.1 decoder causes the content length of an ASN.1 primitive element to be mishandled when it exceeds 2 gigabytes. In the worst case the truncated length is treated as a request to scan the binary content for a terminating zero byte, possibly causing OpenSSL to read either less than or beyond the end of the allocated buffer.
Applications that pass attacker-supplied data to d2i_X509(), d2i_PKCS7(), or any other d2i_* decoding function are affected. OpenSSL's own command-line tools are not vulnerable, as data read through the BIO layer is checked before it reaches the affected code. The issue only affects 64-bit Unix and Unix-like platforms; 32-bit platforms and 64-bit Windows are not affected.
The FIPS modules in 4.0, 3.6, 3.5, 3.4 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.
Affected Products
opensslopensslDetection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Fix
Upgrade the affected component to the fixed release for CVE-2026-34180, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
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 Low impact vulnerability in OpenSSL's ASN.1 decoder affects 64-bit Unix-like platforms, where processing a crafted DER-encoded ASN.1 structure exceeding 2 gigabytes can lead to a heap buffer over-read. This may result in application crashes (Denial of Service) or unintended memory exposure. Red Hat products are…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-34180 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | openssl-1:3.5.5-4.el10_2 | RHSA-2026:25237 |
| Red Hat Enterprise Linux 9 | openssl-1:3.5.5-4.el9_8 | RHSA-2026:25239 |
| Red Hat JBoss Web Server 6.2.5 | jws-optional-native-components-win6-x86_64.zip | RHSA-2026:73982 |
| Cert Manager support for Red Hat OpenShift release 1.20 | cert-manager/cert-manager-trust-manager-rhel9:1790598593 | RHSA-2026:72502 |
| Red Hat Discovery 2 | discovery/discovery-server-rhel9:1782159791 | RHSA-2026:29197 |
| Red Hat Hardened Images | chunkah-main-0.6.0-3.hum1 | RHSA-2026:42825 |
| Red Hat Hardened Images | python-cryptography-main-50.0.0-1.hum1 | RHSA-2026:55543 |
| Red Hat Hardened Images | openssl3-main-3.5.8-0.1.hum1 | RHSA-2026:59635 |
Frequently Asked Questions
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