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CVE-2026-70368

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

6.5 MediumFix available

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".

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
Low

Exploit likelihood

0.35%Unchanged since Aug 5, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.5

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

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".

Record
CVE-2026-70368
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-125
Updated
2026-11-05
EUVDEUVD-2026-52688 6.5

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".

Record
EUVD-2026-52688
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Updated
2026-11-06
GitHub AdvisoriesGHSA-g6w9-m7h7-wgq9 6.5

A stack-based out-of-bounds read vulnerability exists in the "s_vlog" function of stunnel, when...

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".

Record
GHSA-g6w9-m7h7-wgq9
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-125
Updated
2026-11-02
NVD 6.5

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".

Record
CVE-2026-70368
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-125
Updated
2026-11-06
OSVALPINE-CVE-2026-70368 6.5

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".

Record
ALPINE-CVE-2026-70368
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Updated
2026-11-03
OSV 6.5

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

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".

Record
CVE-2026-70368
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-125
Updated
2026-11-07
Show 7 moreShow less
OSVDEBIAN-CVE-2026-70368 6.5

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".

Record
DEBIAN-CVE-2026-70368
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Updated
2026-11-02
OSVAZL-94574 No score

CVE-2026-70368 affecting package stunnel 5.74-1

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".

Record
AZL-94574
Updated
2026-11-05
OSVMGASA-2026-0575 No score

Updated stunnel package fixes security vulnerabilities

Localhost-filter bypass in SOCKS server mode. (CVE-2026-70367) Out-of-bounds memory access when logging long protocol messages. (CVE-2026-70368)

Record
MGASA-2026-0575
Updated
2026-11-05
OSVopenSUSE-SU-2026:11500-1 No score

stunnel-5.80-1.1 on GA media

These are all security issues fixed in the stunnel-5.80-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11500-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:22088-1 No score

Security update for stunnel

This update for stunnel fixes the following issues:

  • CVE-2026-70367: incomplete IP address filtering in SOCKS proxy mode can allow localhost restriction bypasses (bsc#1274207).
  • CVE-2026-70368: oversized log messages in logging routines can cause stack out-of-bounds reads (bsc#1274206).
Record
openSUSE-SU-2026:22088-1
Updated
2026-11-02
OSVSUSE-SU-2026:24232-1 No score

Security update for stunnel

This update for stunnel fixes the following issues:

  • CVE-2026-70367: incomplete IP address filtering in SOCKS proxy mode can allow localhost restriction bypasses (bsc#1274207).
  • CVE-2026-70368: oversized log messages in logging routines can cause stack out-of-bounds reads (bsc#1274206).
Record
SUSE-SU-2026:24232-1
Updated
2026-11-02
OSVSUSE-SU-2026:4617-1 No score

Security update for stunnel

This update for stunnel fixes the following issues:

  • CVE-2026-70367: incomplete IP address filtering in SOCKS proxy mode can allow localhost restriction bypasses (bsc#1274207).
  • CVE-2026-70368: oversized log messages in logging routines can cause stack out-of-bounds reads (bsc#1274206).
Record
SUSE-SU-2026:4617-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
stunnel
Alpine:v3.24
before 5.82-r0
5.82-r0
stunnel
Azure Linux:3
through 5.74-1 None known
stunnel
Debian:14
before 3:5.80-1, plus listed versions
2:3.26-102:3.26-112:3.26-22:3.26-2.12:3.26-3
Show 15 moreShow less
2:3.26-42:3.26-52:3.26-62:3.26-72:3.26-82:3.26-92:3.26-dfsg-12:3.26-dfsg-23.10-0potato13.22-13:5.78-33:5.78-43:5.78-53:5.79-13:5.79-2
3:5.80-1
stunnel4
Debian:12
All versions, plus listed versions
3:5.68-23:5.68-2+deb12u13:5.70-13:5.70-23:5.72-1
Show 10 moreShow less
3:5.72-23:5.72-33:5.72-43:5.73-13:5.74-13:5.74-23:5.76-13:5.77-13:5.78-13:5.78-2
None known
stunnel4
Debian:13
All versions, plus listed versions
3:5.74-23:5.76-13:5.77-13:5.78-13:5.78-2
None known
stunnel
Mageia:10
From an advisory covering 2 CVEs
before 5.80-1.mga10
5.80-1.mga10
stunnel
SUSE:Linux Enterprise Server 16.0
From an advisory covering 2 CVEs
before 5.74-160000.3.1
5.74-160000.3.1
stunnel
SUSE:Linux Enterprise Server for SAP applications 16.0
From an advisory covering 2 CVEs
before 5.74-160000.3.1
5.74-160000.3.1
stunnel
SUSE:Linux Enterprise Module for Server Applications 15 SP7
From an advisory covering 2 CVEs
before 5.70-150600.3.6.1
5.70-150600.3.6.1
stunnel
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
before 5.80-1.1
5.80-1.1
stunnel
openSUSE:Leap 16.0
From an advisory covering 2 CVEs
before 5.74-160000.3.1
5.74-160000.3.1

History

History
RecordedChangedSources
affectedCVE List, EUVD, NVD, OSV
affected, aliases, facts, referencesOSV
affected, aliases, referencesOSV
affected, aliases, products, published, referencesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-70368 is a medium vulnerability (CVSS 6.5) in Microsoft Stunnel, published August 4, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.35%, the 29th percentile. Fixed in stunnel 5.82-r0.

References

Show 16 moreShow less
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