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

> An integer overflow in OpenSSL's ASN.1 string conversion can cause a heap buffer overflow, potentially leading to code execution or crashes in applications using specific custom string types.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Jun 2026
- **Updated:** 10 Jun 2026
- **Also known as:** ALPINE-CVE-2026-7383, AZL-89799, AZL-89858, AZL-89928, BELL-CVE-2026-7383, DEBIAN-CVE-2026-7383, GHSA-w853-v86g-gv7j, JLSEC-2026-1155, MINI-3x76-93xr-jhmv, MINI-p286-c44v-pjpx, ROOT-OS-ALPINE-315-CVE-2026-7383, ROOT-OS-ALPINE-317-CVE-2026-7383, UBUNTU-CVE-2026-7383

## What is CVE-2026-7383?

CVE-2026-7383 is a high-severity vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-7383?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-7383?

Apply the vendor's patch.

## Is CVE-2026-7383 being exploited?

There is no known exploitation of CVE-2026-7383 in the wild and no public exploit code.

## Other vulnerabilities in Openssl Openssl

- [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0)
- [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0)
- [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8)
- [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8)
- [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-7383 and fix it if it is affected.

What it is: CVE-2026-7383 is a high-severity vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-7383 in the wild and no public exploit code.

Affected product: Openssl Openssl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-7383/ (Markdown: https://insights.sbomify.com/CVE-2026-7383/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-7383
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-7383
- OSV: https://osv.dev/vulnerability/CVE-2026-7383

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-7383/
Summaries are generated and may contain mistakes; the official description above is the record.