Possible 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(). When producing Unicode output, the code computes the destination buffer size in a signed int. For BMPSTRING and UNIVERSALSTRING this is done via left-shifting the input character count to account for UTF-16 or UTF-32 width; for UTF8STRING it sums per-character byte counts. With extremely large attacker-controlled input, approximately on the order of 2^30 characters, this size calculation can overflow the signed integer. The overflow can cause an undersized heap allocation; in the worst case for UNIVERSALSTRING, the computed size wraps to zero, OPENSSL_malloc(1) is invoked, and the subsequent copy operation writes far beyond the allocated 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, so no standard network protocol or certificate-handling path exercises the bug.
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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.