CVE-2026-7383 is a high-severity (CVSS 8.1) Out-of-bounds Write vulnerability. A fix is available — see the affected versions and patch details below.
Possible Heap Buffer Overflow in ASN.1 Multibyte String Conversion
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- 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-2026-7383.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-7383 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 380,526 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
Issue summary: A signed integer overflow when sizing the destination buffer for Unicode output in ASN1_mbstring_ncopy() can lead to a heap buffer overflow.
Impact summary: A heap buffer overflow may lead to a crash or possibly attacker controlled code execution or other undefined behaviour.
In ASN1_mbstring_copy() and ASN1_mbstring_ncopy() the destination size for Unicode output is computed in a signed int: by left shift of the input character count for BMPSTRING (UTF-16) and UNIVERSALSTRING (UTF-32), and by summing per-character byte counts for UTF8STRING. The calculation overflows when the input reaches around 2^30 characters. In the worst case (UNIVERSALSTRING at 2^30 characters) the size wraps to zero, OPENSSL_malloc(1) is called, and the subsequent character copy writes several gigabytes past the one-byte allocation.
X.509 certificate processing routes through ASN1_STRING_set_by_NID(), whose DIRSTRING_TYPE mask excludes UNIVERSALSTRING and whose per-NID size limits cap the input length; no network protocol or certificate-handling path in OpenSSL exercises the overflow. Triggering the bug requires an application that calls ASN1_mbstring_copy() or ASN1_mbstring_ncopy() directly, or registers a custom string type via ASN1_STRING_TABLE_add(), with attacker-controlled input on the order of half a gigabyte or more. For these reasons this issue was assigned Low severity.
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-2026-7383, 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
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.
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.
Low impact. This flaw in OpenSSL's ASN1_mbstring_ncopy() function, leading to a heap buffer overflow, is difficult to exploit in typical Red Hat environments. Exploitation requires an application to directly call the vulnerable function with an extremely large, attacker-controlled input (over half a gigabyte), a…
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-2026-7383 (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 |
| 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 |
| Red Hat Hardened Images | openssl-main-3.5.8-0.1.hum1 | RHSA-2026:59641 |
Frequently Asked Questions
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