# CVE-2026-70368: Stunnel: stack-based out-of-bounds read/write in stunnel s_vlog via oversized log message

CVE-2026-70368 is fixed in stunnel on 1 platform, first by DEBIAN-CVE-2026-70368, released August 8, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-70368
- Priority: Routine
- CVSS: 6.5 (Moderate)
- EPSS: 0.0035
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 4, 2026
- Weakness: Out-of-bounds Read
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70368

## Description

A stack-based out-of-bounds read vulnerability exists in the "s_vlog" function of stunnel, when handling oversized log messages via "vsnprintf". A remote attacker with network access to a stunnel service can send protocol inputs that trigger a log message longer than 1024 bytes, leading to an out-of-bounds stack read and a potential crash. In certain corner cases, the same vulnerability could be used to replace a series of trailing "\n" characters with "\0".

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | stunnel Debian 14 | 3:5.80-1 | [DEBIAN-CVE-2026-70368](https://patchblox.com/security/data/fix/linux/debian-cve-2026-70368.md) | Aug 8, 2026 |
| Linux | stunnel opensuse-leap 16.0 | 5.74-160000.3.1 | [OPENSUSE-SU-2026:22088-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-22088-1.md) | Nov 7, 2026 |
| Linux | stunnel sles 15.7 | 5.70-150600.3.6.1 | [SUSE-SU-2026:4617-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4617-1.md) | Nov 7, 2026 |
| Linux | stunnel sles 16.0 | 5.74-160000.3.1 | [SUSE-SU-2026:24232-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-24232-1.md) | Nov 7, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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