Description
stunnel 4.21 through 4.54, when CONNECT protocol negotiation and NTLM authentication are enabled, does not correctly perform integer conversion, which allows remote proxy servers to execute arbitrary code via a crafted request that triggers a buffer overflow.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 13 | stunnel4 | 3:4.53-1.1 | — |
| Debian 12 | stunnel4 | 3:4.53-1.1 | — |
| Debian 6.0 | stunnel4 | 3:4.29-1+squeeze1 | DSA-2664-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 6 | stunnel | 4.29-3.el6_4 | RHSA-2013:0714 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | stunnel | 5.38-1.1 | openSUSE-SU-2024:10289-1 |
Advisories 3
- RHSA-2013:0714 Red Hat Security Advisory: stunnel security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- DSA-2664-1 stunnel4 - buffer overflow Debian Security (DSA / DLA) · Mar 9, 2026
- openSUSE-SU-2024:10289-1 stunnel-5.38-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
References
- MDVSA-2013:130 vendor-advisory
- RHSA-2013:0714 vendor-advisory
- https://www.stunnel.org/CVE-2013-1762.html
- https://wiki.mageia.org/en/Support/Advisories/MGASA-2013-0097
- DSA-2664 vendor-advisory