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

Status: published. Published: 2026-08-04. Updated: 2026-11-05.

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".

## Remediation

- workaround: To mitigate this issue, avoid exposing stunnel services to untrusted clients. Restrict access to these services to trusted networks only. (source: CNA: redhat)

## Affected products and versions

- Mobi-Com Polska Sp. z o.o. / stunnel: ≥ 5.68; < 5.80 (affected, custom). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (stunnel): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.35% as of 2026-11-05; percentile 29.10%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/security/cve/CVE-2026-70368 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2462029 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-70368; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-70368; retrieved 2026-11-05; source updated Not reported

Revision: 16f9922ed106fa68ac29be941b6c5862e8bcd75d63f84288956cabc7f791435b

Canonical: https://y2.dev/cve/CVE-2026-70368

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