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CVE-2026-7383 OpenSSL CVE debrief

A signed integer overflow when sizing the destination buffer for Unicode output in ASN1_mbstring_ncopy() can lead to a heap buffer overflow. This issue impacts applications that call ASN1_mbstring_copy() or ASN1_mbstring_ncopy() directly or register a custom string type via ASN1_STRING_TABLE_add() with attacker-controlled input on the order of half a gigabyte or more.

Vendor
OpenSSL
Product
Unknown
CVSS
HIGH 8.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-09
Original CVE updated
2026-06-16
Advisory published
2026-06-09
Advisory updated
2026-06-16

Who should care

Developers and users of applications that utilize OpenSSL's ASN1_mbstring_copy() or ASN1_mbstring_ncopy() functions, or those that register custom string types via ASN1_STRING_TABLE_add().

Technical summary

The calculation of the destination size for Unicode output in ASN1_mbstring_copy() and ASN1_mbstring_ncopy() overflows when the input reaches around 2^30 characters. In the worst case, this can lead to a call to OPENSSL_malloc(1) followed by a write of several gigabytes past the one-byte allocation.

Defensive priority

Low

Recommended defensive actions

  • Update to the latest version of OpenSSL that includes the fix.
  • Review and update applications that utilize OpenSSL's ASN1_mbstring_copy() or ASN1_mbstring_ncopy() functions, or those that register custom string types via ASN1_STRING_TABLE_add().

Evidence notes

The FIPS modules in OpenSSL versions 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-7383 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-7383

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-7383 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-7383

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.