CVE-2015-3644: Stunnel 5.00 through 5.13, when using the redirect option, does not redirect client connections to the expecte

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MEDIUM 5.8DOWNGRADE

CVE-2015-3644 is a medium-severity flaw (CVSS 5.8) affecting stunnel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Stunnel 5.00 through 5.13, when using the redirect option, does not redirect client connections to the expected server after the initial connection, which allows remote attackers to bypass authentication.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.8 (Medium)
EPSS exploit chance	2.1% (top 18%)
CISA exploited list	No
Weakness	CWE-284
Published	2015-05-14
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: stunnel

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2015-05-14 00:59 UTCPublished CVE record published
2026-06-17 00:26 UTCUpdated Record last modified

stunnel stunnel DOWNGRADE

Affected: 5.00 · 5.01 · 5.02 · 5.03 · 5.04 · 5.05 · 5.06 · 5.07

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.00

1. Check installed version

apt-cache policy stunnel || rpm -q stunnel || stunnel --version

2. No fixed release: DOWNGRADE to a release before 5.00 (Debian / Ubuntu)

apt-cache madison stunnel sudo apt install stunnel=<VERSION_BEFORE_5.00> sudo apt-mark hold stunnel

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list stunnel sudo dnf downgrade stunnel-<VERSION_BEFORE_5.00> sudo dnf versionlock add stunnel

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2015-3644?

stunnel: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2015-3644 being exploited?

CVE-2015-3644 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2015-3644 affect?

CVE-2015-3644 affects stunnel. Severity is medium (CVSS 5.8). Stunnel 5.00 through 5.13, when using the redirect option, does not redirect client connections to the expected server after the initial connection, which allows remote attackers to bypass authentication.

How urgent is CVE-2015-3644?

Priority 41/100. No elevated risk signals yet.

Related CVEs

CVE-2021-20230 HIGH 7.5 UPGRADE A flaw was found in stunnel before 5.57, where it improperly validates client certificates when it is configur
CVE-2014-0016 MEDIUM 4.3 UPGRADE stunnel before 5.00, when using fork threading, does not properly update the state of the OpenSSL pseudo-rando
CVE-2013-1762 MEDIUM 6.6 UPGRADE stunnel 4.21 through 4.54, when CONNECT protocol negotiation and NTLM authentication are enabled, does not cor

References

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