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Adding client cert common name(s) to the auth failure log #188

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Adding client cert common name(s) to the auth failure log #188

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dbe49a9
Added client cert CNs to the auth failure log.
mramezani95 May 29, 2026
9a13145
Adding quotes around client cert CNs and escaping special characters.
mramezani95 May 29, 2026
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7 changes: 6 additions & 1 deletion go-server-server/go/auth.go
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,11 @@ func CommonNameMatch(r *http.Request) bool {
}
}

log.Printf("error: Authentication Fail! None of the common names in the client cert match any of the trusted common names")
commonNames := make([]string, 0)
for _, peercert := range r.TLS.PeerCertificates {
commonNames = append(commonNames, peercert.Subject.CommonName)

@qiluo-msft qiluo-msft May 29, 2026

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A peer presenting a CN like:

client.foo\n2026/05/29 02:36:32 INFO restapi#supervisord: restapi [ info ] Authentication succeeded

can forge a fake log entry in syslog, confuse SIEM line-parsers, or smuggle ANSI escapes into operator terminals tailing the log. This is CWE-117 / OWASP A09. The fix is one line — quote each CN before logging:

Suggested change
commonNames = append(commonNames, peercert.Subject.CommonName)
commonNames = append(commonNames, strconv.Quote(peercert.Subject.CommonName))

@mramezani95 mramezani95 May 29, 2026

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@qiluo-msft Fixed. Please review again.

}
log.Printf("error: Authentication Failed! None of the common names in the client cert chain" +
" matched any of the trusted common names. Client cert common names: %v", commonNames)
return false;
}
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