CVE-2026-70368

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

Published Aug 4, 2026 CVSS 3.1 · 6.5 Medium EPSS < 1% KEV · Not listed
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".

Remediation

Vendor Workaround

To mitigate this issue, avoid exposing stunnel services to untrusted clients. Restrict access to these services to trusted networks only.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Redhat rhel Els
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
cpe:/a:redhat:enterprise_linux:10
cpe:/a:redhat:enterprise_linux:8
cpe:/a:redhat:enterprise_linux:9
cpe:/o:redhat:rhel_els:6
cpe:/o:redhat:rhel_els:7
Vendors & Products Redhat rhel Els
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Stunnel
Stunnel stunnel
Vendors & Products Stunnel
Stunnel stunnel
Type Values Removed Values Added
Title stunnel: Stack-based out-of-bounds read/write in stunnel s_vlog via oversized log message Stunnel: stack-based out-of-bounds read/write in stunnel s_vlog via oversized log message
First Time appeared Redhat
Redhat enterprise Linux
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
References
Type Values Removed Values Added
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".
Title stunnel: Stack-based out-of-bounds read/write in stunnel s_vlog via oversized log message
Weaknesses CWE-125
References
Metrics threat_severity

None

cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L'}

threat_severity

Moderate

Weaknesses

Sources

Status
PUBLISHED
Assigner
redhat
Published
Updated
Nov 5, 2026, 10:51 PM
Reserved
Aug 4, 2026, 7:03 AM
Status
Awaiting Analysis
Published
Aug 4, 2026, 2:16 PM
Modified
Nov 5, 2026, 11:16 PM
Severity
Moderate
Public date
Aug 4, 2026, 10:30 AM