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Add scramMaxIterations option to limit SCRAM iteration count #3677

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Add scramMaxIterations option to limit SCRAM iteration count #3677

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18 changes: 17 additions & 1 deletion packages/pg/lib/client.js
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,17 @@ const queryQueueLengthDeprecationNotice = nodeUtils.deprecate(
'Calling client.query() when the client is already executing a query is deprecated and will be removed in pg@9.0. Use async/await or an external async flow control mechanism instead.'
)

function coerceNumberOrDefault(value, defaultValue) {
if (typeof value === 'number') {
return Number.isFinite(value) ? value : defaultValue
}
if (typeof value === 'string' && value.trim() !== '') {
const n = Number(value)
return Number.isFinite(n) ? n : defaultValue
}
return defaultValue
}

class Client extends EventEmitter {
constructor(config) {
super()
Expand Down Expand Up @@ -74,6 +85,7 @@ class Client extends EventEmitter {
this._txStatus = null

this.enableChannelBinding = Boolean(c.enableChannelBinding) // set true to use SCRAM-SHA-256-PLUS when offered
this.scramMaxIterations = coerceNumberOrDefault(c.scramMaxIterations, sasl.DEFAULT_MAX_SCRAM_ITERATIONS)
this.connection =
c.connection ||
new Connection({
Expand Down Expand Up @@ -307,7 +319,11 @@ class Client extends EventEmitter {
_handleAuthSASL(msg) {
this._getPassword(() => {
try {
this.saslSession = sasl.startSession(msg.mechanisms, this.enableChannelBinding && this.connection.stream)
this.saslSession = sasl.startSession(
msg.mechanisms,
this.enableChannelBinding && this.connection.stream,
this.scramMaxIterations
)
this.connection.sendSASLInitialResponseMessage(this.saslSession.mechanism, this.saslSession.response)
} catch (err) {
this.connection.emit('error', err)
Expand Down
18 changes: 17 additions & 1 deletion packages/pg/lib/crypto/sasl.js
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,9 @@ function saslprep(password) {
return password.replace(nonAsciiSpace, ' ').replace(mappedToNothing, '').normalize('NFKC')
}

function startSession(mechanisms, stream) {
const DEFAULT_MAX_SCRAM_ITERATIONS = 100000

function startSession(mechanisms, stream, scramMaxIterations = DEFAULT_MAX_SCRAM_ITERATIONS) {
const candidates = ['SCRAM-SHA-256']
if (stream) candidates.unshift('SCRAM-SHA-256-PLUS') // higher-priority, so placed first

Expand All @@ -53,6 +55,7 @@ function startSession(mechanisms, stream) {
clientNonce,
response: gs2Header + ',,n=*,r=' + clientNonce,
message: 'SASLInitialResponse',
scramMaxIterations,
}
}

Expand All @@ -78,6 +81,18 @@ async function continueSession(session, password, serverData, stream) {
throw new Error('SASL: SCRAM-SERVER-FIRST-MESSAGE: server nonce is too short')
}

const scramMaxIterations =
typeof session.scramMaxIterations === 'number' ? session.scramMaxIterations : DEFAULT_MAX_SCRAM_ITERATIONS
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@charmander charmander May 14, 2026

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Is session.scramMaxIterations always a number here (at least when used via Client)? If so, I think omitting the check makes sense. (And if supporting direct use really is a goal, startSession seems like the place to do it.)

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@sehrope sehrope May 14, 2026

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Yes it should always be a number as we do the coerceNumberOrDefault(...).

That would simplify it a bit as the only place it's set is in startSession and this part would be just:

  // a value of 0 disables the iteration count check
  if (this.scramMaxIterations !== 0 && sv.iteration > this.scramMaxIterations) {
    throw new Error(
      'SASL: SCRAM-SERVER-FIRST-MESSAGE: iteration count ' +
        sv.iteration +
        ' exceeds scramMaxIterations of ' +
        this.scramMaxIterations
    )
  }

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@sehrope sehrope May 14, 2026 •
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Oh wait I realize now that I did it like this because a bunch of the tests create their own session objects and call the other sasl functions:

sasl.continueSession(
    {
      message: 'SASLInitialResponse',
      clientNonce: 'a',
    },
    badPasswordValue,
    'r=1,i=1'
  ),
  {
    message: 'SASL: SCRAM-SERVER-FIRST-MESSAGE: client password must be a string',
  }
)

So it wouldn't always be populated unless we update all the tests to add the default.

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@charmander charmander May 14, 2026

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Maybe a shared wrapper function for test use that’s more faithful to how Client will use it?

// a value of 0 disables the iteration count check
if (scramMaxIterations !== 0 && sv.iteration > scramMaxIterations) {
throw new Error(
'SASL: SCRAM-SERVER-FIRST-MESSAGE: iteration count ' +
sv.iteration +
' exceeds scramMaxIterations of ' +
scramMaxIterations
)
}

const clientFirstMessageBare = 'n=*,r=' + session.clientNonce
const serverFirstMessage = 'r=' + sv.nonce + ',s=' + sv.salt + ',i=' + sv.iteration

Expand Down Expand Up @@ -243,4 +258,5 @@ module.exports = {
startSession,
continueSession,
finalizeSession,
DEFAULT_MAX_SCRAM_ITERATIONS,
}
74 changes: 74 additions & 0 deletions packages/pg/test/unit/client/sasl-scram-tests.js
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Expand Up @@ -55,6 +55,18 @@ suite.test('sasl/scram', function () {

assert(session1.clientNonce != session2.clientNonce)
})

suite.test('defaults scramMaxIterations to 100000', function () {
const session = sasl.startSession(['SCRAM-SHA-256'])

assert.equal(session.scramMaxIterations, 100000)
})

suite.test('honors a custom scramMaxIterations', function () {
const session = sasl.startSession(['SCRAM-SHA-256'], null, 50)

assert.equal(session.scramMaxIterations, 50)
})
})

suite.test('continueSession', function () {
Expand Down Expand Up @@ -159,6 +171,68 @@ suite.test('sasl/scram', function () {
)
})

suite.test('fails when iteration count exceeds default scramMaxIterations', async function () {
await assert.rejects(
function () {
return sasl.continueSession(
{
message: 'SASLInitialResponse',
clientNonce: 'a',
scramMaxIterations: 100000,
},
'password',
'r=ab,s=abcd,i=100001'
)
},
{
message: 'SASL: SCRAM-SERVER-FIRST-MESSAGE: iteration count 100001 exceeds scramMaxIterations of 100000',
}
)
})

suite.test('fails when iteration count exceeds a custom scramMaxIterations', async function () {
await assert.rejects(
function () {
return sasl.continueSession(
{
message: 'SASLInitialResponse',
clientNonce: 'a',
scramMaxIterations: 10,
},
'password',
'r=ab,s=abcd,i=11'
)
},
{
message: 'SASL: SCRAM-SERVER-FIRST-MESSAGE: iteration count 11 exceeds scramMaxIterations of 10',
}
)
})

suite.test('allows iteration count at the scramMaxIterations limit', async function () {
const session = {
message: 'SASLInitialResponse',
clientNonce: 'a',
scramMaxIterations: 5,
}

await sasl.continueSession(session, 'password', 'r=ab,s=abcd,i=5')

assert.equal(session.message, 'SASLResponse')
})

suite.test('disables the iteration count check when scramMaxIterations is 0', async function () {
const session = {
message: 'SASLInitialResponse',
clientNonce: 'a',
scramMaxIterations: 0,
}

await sasl.continueSession(session, 'password', 'r=ab,s=abcd,i=999999')

assert.equal(session.message, 'SASLResponse')
})

suite.test('sets expected session data (SCRAM-SHA-256)', async function () {
const session = {
message: 'SASLInitialResponse',
Expand Down
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