Heap Buffer Overflow in OpenSSL ASN.1 Multibyte String Conversion
CVE-2026-7383 is a low-severity vulnerability in OpenSSL's ASN.1 multibyte string conversion logic, specifically in ASN1_mbstring_copy() and ASN1_mbstring_ncopy(). The flaw is caused by a signed integer overflow when calculating the destination buffer size for Unicode output. For BMPSTRING (UTF-16) and UNIVERSALSTRING (UTF-32), the size is derived by left-shifting the input character count; for UTF8STRING, the size is accumulated from per-character byte counts. When the input reaches roughly 2^30 characters, the signed int used for sizing can overflow. In the worst case, a UNIVERSALSTRING input of about 2^30 characters causes the computed size to wrap to zero, resulting in OPENSSL_malloc(1) followed by a copy operation that writes far beyond the allocated heap buffer. OpenSSL states that normal X.509 certificate processing does not reach this condition because ASN1_STRING_set_by_NID() applies DIRSTRING_TYPE restrictions and per-NID length limits, excluding the dangerous UNIVERSALSTRING path in certificate handling.
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Exploits
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No public exploit code observed for this vulnerability.
Affected products & vendors
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Recent activity
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.