vulnerability / NVI-00016333 / Revision 1
Mailpit: SMTP command parser buffers unbounded command lines before syntax rejection
GitHub lists this reviewed advisory for github.com/axllent/mailpit. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
github.com/axllent/mailpit
source listed<= 1.30.3
## Summary Mailpit's SMTP server reads each command line with an unbounded `bufio.Reader.ReadString('\n')` before parsing the command or enforcing any protocol length limit. A remote SMTP client can send an oversized single command line and force Mailpit to allocate attacker-controlled memory before the server returns a syntax error or times out, even though RFC 5321 limits SMTP command lines to 512 octets including CRLF. ## Technical Details Mailpit enables SMTP by default. `config/config.go` sets `SMTPListen = "[::]:1025"`, and `cmd/root.go` calls `smtpd.Listen()` during normal startup. The SMTP server configures recipient and message DATA size limits in `internal/smtpd/main.go`, including the default 50 MiB `MaxMessageSize`, but those limits do not apply to command lines. The vulnerable path is in the SMTP command loop. `internal/smtpd/smtpd.go` calls `s.readLine()` for every command before parsing the verb or arguments: ```go line, err := s.readLine() if err != nil { if netErr, ok := err.(net.Error); ok && netErr.Timeout() { s.writef("421 4.4.2 %s %s ESMTP Service closing transmission channel after timeout exceeded", s.srv.Hostname, s.srv.AppName) } bre
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-w878-pj84-3j5v ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.