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fix(security): use CSPRNG for password and OTP generation #3477

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fix(security): use CSPRNG for password and OTP generation #3477

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4 changes: 2 additions & 2 deletions apps/sim/app/api/chat/[identifier]/otp/route.ts
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
import { randomUUID } from 'crypto'
import { randomInt, randomUUID } from 'crypto'
import { db } from '@sim/db'
import { chat, verification } from '@sim/db/schema'
import { createLogger } from '@sim/logger'
Expand All @@ -17,7 +17,7 @@ import { createErrorResponse, createSuccessResponse } from '@/app/api/workflows/
const logger = createLogger('ChatOtpAPI')

function generateOTP() {
return Math.floor(100000 + Math.random() * 900000).toString()
return randomInt(100000, 1000000).toString()
}

const OTP_EXPIRY = 15 * 60 // 15 minutes
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3 changes: 2 additions & 1 deletion apps/sim/lib/core/security/encryption.ts
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Expand Up @@ -76,8 +76,9 @@ export function generatePassword(length = 24): string {
const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()_-+='
let result = ''

const bytes = randomBytes(length)
for (let i = 0; i < length; i++) {
result += chars.charAt(Math.floor(Math.random() * chars.length))
result += chars.charAt(bytes[i] % chars.length)
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@cursor cursor bot Mar 9, 2026

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Modulo bias in cryptographic password generation

Medium Severity

bytes[i] % chars.length introduces modulo bias because 256 is not evenly divisible by 76 (the charset length). The first 28 characters have a ~33% higher chance of being selected than the remaining 48 characters, reducing the effective entropy of generated passwords. Ironically, this PR aims to improve cryptographic security but introduces a well-known CSPRNG pitfall. crypto.randomInt(0, chars.length) avoids this by using rejection sampling internally.

Fix in Cursor Fix in Web

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@greptile-apps greptile-apps bot Mar 9, 2026

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Modulo bias reduces character distribution uniformity

bytes[i] % chars.length introduces a modulo bias because 256 is not evenly divisible by chars.length (76). This means the first 256 % 76 = 28 characters in the charset each have a slightly higher probability of selection (4/256) than the remaining characters (3/256), rather than the ideal uniform 1/76.

While this is astronomically more secure than Math.random(), a password generator should strive for uniform distribution. randomInt (already imported in the OTP route) performs rejection sampling internally and provides a perfectly uniform result:

for (let i = 0; i < length; i++) {
  result += chars.charAt(randomInt(0, chars.length))
}

Note that randomBytes would no longer be needed for this function (though it remains used elsewhere in the file).

}

return result
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