Possible Heap Buffer Overflow in ASN.1 Multibyte String Conversion

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Summary

CVECVE-2026-7383
StatePUBLISHED
Assigneropenssl
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-09 17:17:50 UTC
Updated2026-06-10 08:16:25 UTC
DescriptionIssue 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.

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from ADP

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Problem Types: CWE-787 | CWE-787 CWE-787 Out-of-bounds Write

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED8.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary8.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA OpenSSL OpenSSL affected 4.0.0 4.0.1 semver Not specified
CNA OpenSSL OpenSSL affected 3.6.0 3.6.3 semver Not specified
CNA OpenSSL OpenSSL affected 3.5.0 3.5.7 semver Not specified
CNA OpenSSL OpenSSL affected 3.4.0 3.4.6 semver Not specified
CNA OpenSSL OpenSSL affected 3.0.0 3.0.21 semver Not specified
CNA OpenSSL OpenSSL affected 1.1.1 1.1.1zh custom Not specified
CNA OpenSSL OpenSSL affected 1.0.2 1.0.2zq custom Not specified

References

ReferenceSourceLinkTags
github.com/openssl/openssl/commit/4f8d2bddaa2c8e06f9c33390ee1717059a6e4be6 [email protected] github.com
github.com/openssl/openssl/commit/bd17511070fb39a67bfa19682affb765e706a974 [email protected] github.com
github.com/openssl/openssl/commit/c332adaced43bcbb85f97410597e951c11ec3083 [email protected] github.com
github.com/openssl/openssl/commit/80c15faaf78042bbb8654a0e234c50c381732f74 [email protected] github.com
openssl-library.org/news/secadv/20260609.txt [email protected] openssl-library.org
github.com/openssl/openssl/commit/d32350ae8ef7426718f5aa9e383d4b51398ee255 [email protected] github.com
github.com/openssl/security/commit/4f8d2bddaa2c8e06f9c33390ee1717059a6e4be6 MITRE github.com
github.com/openssl/security/commit/80c15faaf78042bbb8654a0e234c50c381732f74 MITRE github.com
github.com/openssl/security/commit/bd17511070fb39a67bfa19682affb765e706a974 MITRE github.com
github.com/openssl/security/commit/c332adaced43bcbb85f97410597e951c11ec3083 MITRE github.com
github.com/openssl/security/commit/d32350ae8ef7426718f5aa9e383d4b51398ee255 MITRE github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Zehua Qiao (en)

CNA: Jinwen He (en)

CNA: Viktor Dukhovni (en)

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