CVE-2026-7383 | Possible Heap Buffer Overflow in ASN.1 Multibyte String Conversion

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.

Published: 2026-06-09 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-7383 is rated Moderate Risk (42.1/100): CVSS High severity, with low exploitation likelihood (EPSS 0.36%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-7383

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-18 0.32% 0.36% +0.03%
2 2026-06-15 0.07% 0.32% +0.26%
3 2026-06-10 — 0.07% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-7383

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.1 3.1 HIGH
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-7383

GitHub Security Advisory for CVE-2026-7383

GHSA-w853-v86g-gv7j · Severity: high — Issue summary: A signed integer overflow when sizing the destination buffer for Unicode output in...

OS Trackers for CVE-2026-7383

vendor priority summary link
debian not yet assigned CVE-2026-7383 not yet assigned priority: Debian including 1 source packages (openssl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-7383
redhat low — https://access.redhat.com/security/cve/CVE-2026-7383
suse medium CVE-2026-7383 severity moderate: SUSE including 70 source package names (latest:libexpat1-2.7.1-4.1, latest:libopenssl3-3.1.4-slfo.1.1_10.1, …), 364 product×package rows across 68 product lines (Container suse/sl-micro/6.0/baremetal-os-container, Container suse/sl-micro/6.0/base-os-container, … (68 product lines)): First Fixed 240, Fixed 69, Known Not Affected 55. https://www.suse.com/security/cve/CVE-2026-7383/
ubuntu low CVE-2026-7383 low priority: Ubuntu including 5 source packages (edk2, nodejs, openssl, openssl-fips, openssl1.0), 35 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): needs-triage 12, released 9, DNE 8, not-affected 5, needed 1. https://ubuntu.com/security/CVE-2026-7383

Affected software / configurations for CVE-2026-7383

Vendor Product Version Raw CPE
openssl openssl >= 1.0.2, < 1.0.2zq cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 1.1.1, < 1.1.1zh cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.0.0, < 3.0.21 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.4.0, < 3.4.6 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.5.0, < 3.5.7 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.6.0, < 3.6.3 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl 4.0.0 cpe:2.3:a:openssl:openssl:4.0.0:-:*:*:*:*:*:*

References for CVE-2026-7383

cvelogic Threat Intelligence