PatchTheCVECVE-2020-15955: In s/qmail through 4.0.07, an active MitM can inject arbitrary plaintext commands into a STARTTLS encrypted se
CVE-2020-15955 is a medium-severity flaw (CVSS 5.9) affecting s\/qmail. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
In s/qmail through 4.0.07, an active MitM can inject arbitrary plaintext commands into a STARTTLS encrypted session between an SMTP client and s/qmail. This allows e-mail messages and user credentials to be sent to the MitM attacker.
Why this priority
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 5.9 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | High |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.9% (top 39%) |
| CISA exploited list | No |
| Weakness | CWE-77 |
| Published | 2021-08-17 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
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-2020-15955?
s\/qmail: upgrade to newer than 4.0.07. Exact commands for each OS are on this page.
Is CVE-2020-15955 being exploited?
CVE-2020-15955 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-2020-15955 affect?
CVE-2020-15955 affects s\/qmail. Severity is medium (CVSS 5.9). In s/qmail through 4.0.07, an active MitM can inject arbitrary plaintext commands into a STARTTLS encrypted session between an SMTP client and s/qmail. This allows e-mail messages and user credentials to be sent to the MitM attacker.
How urgent is CVE-2020-15955?
Priority 41/100. Remotely exploitable, no login, no user action