1
0
mirror of https://blitiri.com.ar/repos/chasquid synced 2026-10-29 15:02:30 +00:00
Files
go-chasquid-smtp/internal/dkim/verify_test.go
T
Alberto Bertogli b153955d5d dkim: Fix work amplification on h= tag processing
When verifying emails, for each entry in the h= tag, we would scan all
headers, leading to quadratic behaviour.

Similarly, when signing, for each instance of a signed header we would
scan all headers.

This could lead to unauthenticated DoS via work amplification.

This patch fixes the problem by going through the headers only once, so
behaviour is now linear, and also limiting the size of the h= tag for
defense in depth.

The limit is in line with what other implementations use, so it should
not cause any interoperability problems.

Thanks to John JEAN <john@wargan.com> for finding and reporting this
problem. The detailed report can be found in
https://johnjean.io/advisories/chasquid-unauthenticated-remote-dos/.
2026-10-09 21:34:10 +01:00

523 lines
16 KiB
Go

package dkim
import (
"context"
"crypto"
"encoding/base64"
"errors"
"fmt"
"net"
"strings"
"testing"
"github.com/google/go-cmp/cmp"
)
func toCRLF(s string) string {
return strings.ReplaceAll(s, "\n", "\r\n")
}
func makeLookupTXT(results map[string][]string) lookupTXTFunc {
return func(ctx context.Context, domain string) ([]string, error) {
return results[domain], nil
}
}
func TestVerifyRF6376CExample(t *testing.T) {
ctx := t.Context()
ctx = WithTraceFunc(ctx, t.Logf)
// Use the public key from the example in RFC 6376 appendix C.
// https://datatracker.ietf.org/doc/html/rfc6376#appendix-C
ctx = WithLookupTXTFunc(ctx, makeLookupTXT(map[string][]string{
"brisbane._domainkey.example.com": {
"v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQ" +
"KBgQDwIRP/UC3SBsEmGqZ9ZJW3/DkMoGeLnQg1fWn7/zYt" +
"IxN2SnFCjxOCKG9v3b4jYfcTNh5ijSsq631uBItLa7od+v" +
"/RtdC2UzJ1lWT947qR+Rcac2gbto/NMqJ0fzfVjH4OuKhi" +
"tdY9tf6mcwGjaNBcWToIMmPSPDdQPNUYckcQ2QIDAQAB",
},
}))
// Note that the examples in the RFC text have multiple issues:
// - The double space in "game. Are" should be a single
// space. Otherwise, the body hash does not match.
// https://www.rfc-editor.org/errata/eid3192
// - The header indentation is incorrect. This causes
// signature validation failure (because the example uses simple
// canonicalization, which leaves the indentation untouched).
// https://www.rfc-editor.org/errata/eid4926
message := toCRLF(
`DKIM-Signature: v=1; a=rsa-sha256; s=brisbane; d=example.com;
c=simple/simple; q=dns/txt; i=joe@football.example.com;
h=Received : From : To : Subject : Date : Message-ID;
bh=2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8=;
b=AuUoFEfDxTDkHlLXSZEpZj79LICEps6eda7W3deTVFOk4yAUoqOB
4nujc7YopdG5dWLSdNg6xNAZpOPr+kHxt1IrE+NahM6L/LbvaHut
KVdkLLkpVaVVQPzeRDI009SO2Il5Lu7rDNH6mZckBdrIx0orEtZV
4bmp/YzhwvcubU4=;
Received: from client1.football.example.com [192.0.2.1]
by submitserver.example.com with SUBMISSION;
Fri, 11 Jul 2003 21:01:54 -0700 (PDT)
From: Joe SixPack <joe@football.example.com>
To: Suzie Q <suzie@shopping.example.net>
Subject: Is dinner ready?
Date: Fri, 11 Jul 2003 21:00:37 -0700 (PDT)
Message-ID: <20030712040037.46341.5F8J@football.example.com>
Hi.
We lost the game. Are you hungry yet?
Joe.
`)
res, err := VerifyMessage(ctx, message)
if res.Valid != 1 || err != nil {
t.Errorf("VerifyMessage: wanted 1 valid / nil; got %v / %v", res, err)
}
// Extend the message, check it does not pass validation.
res, err = VerifyMessage(ctx, message+"Extra line.\r\n")
if res.Valid != 0 || err != nil {
t.Errorf("VerifyMessage: wanted 0 valid / nil; got %v / %v", res, err)
}
// Alter a header, check it does not pass validation.
res, err = VerifyMessage(ctx,
strings.Replace(message, "Subject", "X-Subject", 1))
if res.Valid != 0 || err != nil {
t.Errorf("VerifyMessage: wanted 0 valid / nil; got %v / %v", res, err)
}
}
func TestVerifyRFC8463Example(t *testing.T) {
ctx := t.Context()
ctx = WithTraceFunc(ctx, t.Logf)
// Use the public keys from the example in RFC 8463 appendix A.2.
// https://datatracker.ietf.org/doc/html/rfc6376#appendix-C
ctx = WithLookupTXTFunc(ctx, makeLookupTXT(map[string][]string{
"brisbane._domainkey.football.example.com": {
"v=DKIM1; k=ed25519; " +
"p=11qYAYKxCrfVS/7TyWQHOg7hcvPapiMlrwIaaPcHURo="},
"test._domainkey.football.example.com": {
"v=DKIM1; k=rsa; " +
"p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDkHlOQoBTzWR" +
"iGs5V6NpP3idY6Wk08a5qhdR6wy5bdOKb2jLQiY/J16JYi0Qvx/b" +
"yYzCNb3W91y3FutACDfzwQ/BC/e/8uBsCR+yz1Lxj+PL6lHvqMKr" +
"M3rG4hstT5QjvHO9PzoxZyVYLzBfO2EeC3Ip3G+2kryOTIKT+l/K" +
"4w3QIDAQAB"},
}))
message := toCRLF(
`DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed;
d=football.example.com; i=@football.example.com;
q=dns/txt; s=brisbane; t=1528637909; h=from : to :
subject : date : message-id : from : subject : date;
bh=2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8=;
b=/gCrinpcQOoIfuHNQIbq4pgh9kyIK3AQUdt9OdqQehSwhEIug4D11Bus
Fa3bT3FY5OsU7ZbnKELq+eXdp1Q1Dw==
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=football.example.com; i=@football.example.com;
q=dns/txt; s=test; t=1528637909; h=from : to : subject :
date : message-id : from : subject : date;
bh=2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8=;
b=F45dVWDfMbQDGHJFlXUNB2HKfbCeLRyhDXgFpEL8GwpsRe0IeIixNTe3
DhCVlUrSjV4BwcVcOF6+FF3Zo9Rpo1tFOeS9mPYQTnGdaSGsgeefOsk2Jz
dA+L10TeYt9BgDfQNZtKdN1WO//KgIqXP7OdEFE4LjFYNcUxZQ4FADY+8=
From: Joe SixPack <joe@football.example.com>
To: Suzie Q <suzie@shopping.example.net>
Subject: Is dinner ready?
Date: Fri, 11 Jul 2003 21:00:37 -0700 (PDT)
Message-ID: <20030712040037.46341.5F8J@football.example.com>
Hi.
We lost the game. Are you hungry yet?
Joe.
`)
expected := &VerifyResult{
Found: 2,
Valid: 2,
Results: []*OneResult{
{
SignatureHeader: toCRLF(
` v=1; a=ed25519-sha256; c=relaxed/relaxed;
d=football.example.com; i=@football.example.com;
q=dns/txt; s=brisbane; t=1528637909; h=from : to :
subject : date : message-id : from : subject : date;
bh=2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8=;
b=/gCrinpcQOoIfuHNQIbq4pgh9kyIK3AQUdt9OdqQehSwhEIug4D11Bus
Fa3bT3FY5OsU7ZbnKELq+eXdp1Q1Dw==`),
Domain: "football.example.com",
Selector: "brisbane",
B: "/gCrinpcQOoIfuHNQIbq4pgh9kyIK3AQUdt9OdqQehSwhEIug4D11" +
"BusFa3bT3FY5OsU7ZbnKELq+eXdp1Q1Dw==",
State: SUCCESS,
Error: nil,
},
{
SignatureHeader: toCRLF(
` v=1; a=rsa-sha256; c=relaxed/relaxed;
d=football.example.com; i=@football.example.com;
q=dns/txt; s=test; t=1528637909; h=from : to : subject :
date : message-id : from : subject : date;
bh=2jUSOH9NhtVGCQWNr9BrIAPreKQjO6Sn7XIkfJVOzv8=;
b=F45dVWDfMbQDGHJFlXUNB2HKfbCeLRyhDXgFpEL8GwpsRe0IeIixNTe3
DhCVlUrSjV4BwcVcOF6+FF3Zo9Rpo1tFOeS9mPYQTnGdaSGsgeefOsk2Jz
dA+L10TeYt9BgDfQNZtKdN1WO//KgIqXP7OdEFE4LjFYNcUxZQ4FADY+8=`),
Domain: "football.example.com",
Selector: "test",
B: "F45dVWDfMbQDGHJFlXUNB2HKfbCeLRyhDXgFpEL8GwpsRe0IeIixNTe" +
"3DhCVlUrSjV4BwcVcOF6+FF3Zo9Rpo1tFOeS9mPYQTnGdaSGsgeefO" +
"sk2JzdA+L10TeYt9BgDfQNZtKdN1WO//KgIqXP7OdEFE4LjFYNcUxZ" +
"Q4FADY+8=",
State: SUCCESS,
Error: nil,
},
},
}
res, err := VerifyMessage(ctx, message)
if err != nil {
t.Fatalf("VerifyMessage returned error: %v", err)
}
if diff := cmp.Diff(expected, res); diff != "" {
t.Errorf("VerifyMessage diff (-want +got):\n%s", diff)
}
// Extend the message, check it does not pass validation.
res, err = VerifyMessage(ctx, message+"Extra line.\r\n")
if res.Found != 2 || res.Valid != 0 || err != nil {
t.Errorf("VerifyMessage: wanted 2 found, 0 valid / nil; got %v / %v",
res, err)
}
// Alter a header, check it does not pass validation.
res, err = VerifyMessage(ctx,
strings.Replace(message, "Subject", "X-Subject", 1))
if res.Found != 2 || res.Valid != 0 || err != nil {
t.Errorf("VerifyMessage: wanted 2 found, 0 valid / nil; got %v / %v",
res, err)
}
}
func TestVerifyBodyLength(t *testing.T) {
ctx := t.Context()
ctx = WithTraceFunc(ctx, t.Logf)
// Any valid key works, since none of the signatures here are valid. We
// use the one from the example in RFC 8463 appendix A.2.
ctx = WithLookupTXTFunc(ctx, makeLookupTXT(map[string][]string{
"brisbane._domainkey.example.com": {
"v=DKIM1; k=ed25519; " +
"p=11qYAYKxCrfVS/7TyWQHOg7hcvPapiMlrwIaaPcHURo="},
}))
// Use a valid body hash (of the "signed" part of the body), so we can
// tell the l= cases apart: when l= covers exactly the signed part, the
// body hash matches and we fail later on (because b= is bogus).
body := "Hi.\r\n"
cases := []struct {
l string
signed string
want error
}{
{"0", "", ErrVerificationFailed},
{"0", body, ErrBodyHashMismatch},
{"4", body, ErrBodyHashMismatch},
{"5", body, ErrVerificationFailed},
{"6", body, errInvalidTag},
{"18446744073709551615", body, errInvalidTag},
}
for _, c := range cases {
bh := base64.StdEncoding.EncodeToString(
hashWith(crypto.SHA256, []byte(c.signed)))
message := toCRLF(
"DKIM-Signature: v=1; a=ed25519-sha256; c=simple/simple;\n"+
" d=example.com; s=brisbane; h=from; l="+c.l+";\n"+
" bh="+bh+"; b=AAAA\n"+
"From: Joe SixPack <joe@example.com>\n"+
"\n") + body
res, err := VerifyMessage(ctx, message)
if err != nil {
t.Fatalf("l=%s signed=%q: VerifyMessage returned error: %v",
c.l, c.signed, err)
}
if res.Found != 1 || res.Valid != 0 {
t.Fatalf("l=%s signed=%q: wanted 1 found, 0 valid; got %v",
c.l, c.signed, res)
}
r := res.Results[0]
if r.State != PERMFAIL || !errors.Is(r.Error, c.want) {
t.Errorf("l=%s signed=%q: wanted PERMFAIL / %v; got %v / %v",
c.l, c.signed, c.want, r.State, r.Error)
}
}
}
func TestHeadersToInclude(t *testing.T) {
// Test that headersToInclude returns the expected headers.
cases := []struct {
sigH header
hTag []string
headers headers
want []header
}{
// Check that if a header appears more than once, we pick the latest
// first.
{
sigH: header{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=brisbane; d=example.com;",
},
hTag: []string{"From", "To", "Subject"},
headers: headers{
{Name: "From", Value: "from1"},
{Name: "To", Value: "to1"},
{Name: "Subject", Value: "subject1"},
{Name: "From", Value: "from2"},
},
want: []header{
{Name: "From", Value: "from2"},
{Name: "To", Value: "to1"},
{Name: "Subject", Value: "subject1"},
},
},
// Check that if a header is requested twice but only appears once, we
// only return it once.
// This is a common technique suggested by the RFC to make signatures
// fail if a header is added.
{
sigH: header{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=brisbane; d=example.com;",
},
hTag: []string{"From", "From", "To", "Subject"},
headers: headers{
{Name: "From", Value: "from1"},
{Name: "To", Value: "to1"},
{Name: "Subject", Value: "subject1"},
},
want: []header{
{Name: "From", Value: "from1"},
{Name: "To", Value: "to1"},
{Name: "Subject", Value: "subject1"},
},
},
// Check that if DKIM-Signature is included, we do *not* include the
// one we're currently verifying in the headers to include.
// https://datatracker.ietf.org/doc/html/rfc6376#section-3.7
{
sigH: header{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=brisbane; d=example.com;",
},
hTag: []string{"From", "From", "DKIM-Signature", "DKIM-Signature"},
headers: headers{
{Name: "From", Value: "from1"},
{Name: "To", Value: "to1"},
{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=sidney; d=example.com;",
},
{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=brisbane; d=example.com;",
},
},
want: []header{
{Name: "From", Value: "from1"},
{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=sidney; d=example.com;",
},
},
},
// Check that header names are compared case-insensitively, and that
// headers that are not present are skipped.
{
sigH: header{
Name: "DKIM-Signature",
Value: "v=1; a=rsa-sha256; s=brisbane; d=example.com;",
},
hTag: []string{"from", "X-Missing", "FROM", "subject"},
headers: headers{
{Name: "FROM", Value: "from1"},
{Name: "Subject", Value: "subject1"},
{Name: "From", Value: "from2"},
},
want: []header{
{Name: "From", Value: "from2"},
{Name: "FROM", Value: "from1"},
{Name: "Subject", Value: "subject1"},
},
},
}
for _, c := range cases {
got := headersToInclude(c.sigH, c.hTag, c.headers)
if diff := cmp.Diff(c.want, got); diff != "" {
t.Errorf("headersToInclude(%q, %v, %v) diff (-want +got):\n%s",
c.sigH, c.hTag, c.headers, diff)
}
}
}
func TestHeadersToIncludeLarge(t *testing.T) {
// Regression test for a DoS where headersToInclude was O(len(h=) *
// len(headers)), which with large (attacker-controlled) inputs could take
// hours. This takes milliseconds, while the quadratic implementation
// took minutes with this input. We don't check the timing, so a
// regression will show up as this test being very slow.
const n = 100_000
sigH := header{Name: "DKIM-Signature", Value: "v=1;"}
hTag := make([]string, n)
hdrs := make(headers, n)
for i := range n {
hTag[i] = "a"
hdrs[i] = header{Name: "a", Value: fmt.Sprint(i)}
}
got := headersToInclude(sigH, hTag, hdrs)
if len(got) != n {
t.Fatalf("wanted %d headers, got %d", n, len(got))
}
// Last instance first.
if got[0].Value != fmt.Sprint(n-1) || got[n-1].Value != "0" {
t.Errorf("unexpected order: first %q, last %q",
got[0].Value, got[n-1].Value)
}
}
func TestAuthenticationResults(t *testing.T) {
resBrisbane := &OneResult{
Domain: "football.example.com",
Selector: "brisbane",
B: "/gCrinpcQOoIfuHNQIbq4pgh9kyIK3AQUdt9OdqQehSwhEIug4D11" +
"BusFa3bT3FY5OsU7ZbnKELq+eXdp1Q1Dw==",
State: SUCCESS,
Error: nil,
}
resTest := &OneResult{
Domain: "football.example.com",
Selector: "test",
B: "F45dVWDfMbQDGHJFlXUNB2HKfbCeLRyhDXgFpEL8GwpsRe0IeIixNTe" +
"3DhCVlUrSjV4BwcVcOF6+FF3Zo9Rpo1tFOeS9mPYQTnGdaSGsgeefO" +
"sk2JzdA+L10TeYt9BgDfQNZtKdN1WO//KgIqXP7OdEFE4LjFYNcUxZ" +
"Q4FADY+8=",
State: SUCCESS,
Error: nil,
}
resFail := &OneResult{
Domain: "football.example.com",
Selector: "paris",
B: "slfkdMSDFeslif39seFfjl93sljisdsdlif923l",
State: PERMFAIL,
Error: ErrVerificationFailed,
}
resPermFail := &OneResult{
Domain: "football.example.com",
Selector: "paris",
// No B tag on purpose.
State: PERMFAIL,
Error: errMissingRequiredTag,
}
resTempFail := &OneResult{
Domain: "football.example.com",
Selector: "paris",
B: "shorty", // Less than 12 characters to check we include it well.
State: TEMPFAIL,
Error: &net.DNSError{
Err: "dns temp error (for testing)",
IsTemporary: true,
},
}
cases := []struct {
results *VerifyResult
want string
}{
{
results: &VerifyResult{},
want: ";dkim=none\r\n",
},
{
results: &VerifyResult{
Found: 1,
Valid: 1,
Results: []*OneResult{resBrisbane},
},
want: ";dkim=pass" +
" header.b=/gCrinpcQOoI header.d=football.example.com\r\n",
},
{
results: &VerifyResult{
Found: 2,
Valid: 2,
Results: []*OneResult{resBrisbane, resTest},
},
want: ";dkim=pass" +
" header.b=/gCrinpcQOoI header.d=football.example.com\r\n" +
";dkim=pass" +
" header.b=F45dVWDfMbQD header.d=football.example.com\r\n",
},
{
results: &VerifyResult{
Found: 2,
Valid: 2,
Results: []*OneResult{resBrisbane, resTest},
},
want: ";dkim=pass" +
" header.b=/gCrinpcQOoI header.d=football.example.com\r\n" +
";dkim=pass" +
" header.b=F45dVWDfMbQD header.d=football.example.com\r\n",
},
{
results: &VerifyResult{
Found: 2,
Valid: 1,
Results: []*OneResult{resFail, resTest},
},
want: ";dkim=fail reason=\"verification failed\"\r\n" +
" header.b=slfkdMSDFesl header.d=football.example.com\r\n" +
";dkim=pass" +
" header.b=F45dVWDfMbQD header.d=football.example.com\r\n",
},
{
results: &VerifyResult{
Found: 1,
Results: []*OneResult{resPermFail},
},
want: ";dkim=permerror reason=\"missing required tag\"\r\n" +
" header.d=football.example.com\r\n",
},
{
results: &VerifyResult{
Found: 1,
Results: []*OneResult{resTempFail},
},
want: ";dkim=temperror reason=\"lookup : dns temp error (for testing)\"\r\n" +
" header.b=shorty header.d=football.example.com\r\n",
},
}
for i, c := range cases {
got := c.results.AuthenticationResults()
if diff := cmp.Diff(c.want, got); diff != "" {
t.Errorf("case %d: AuthenticationResults() diff (-want +got):\n%s",
i, diff)
}
}
}