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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[Security] SCRAM-SHA-256 accepts dangerously low iteration count from server","articleBody":"Split from #3651 as suggested by @charmander.\n\n## Summary\n\nThe SCRAM-SHA-256 implementation accepts any iteration count \u003e= 1 from the server. A rogue PostgreSQL server can send a SCRAM challenge with `i=1`, making the derived key trivially cheap to brute-force offline.\n\n## Affected code\n\n`packages/pg/lib/crypto/sasl.js` — `parseServerFirstMessage()`:\n\n```js\nconst iterationText = attrPairs.get('i')\nif (!iterationText) {\n  throw new Error('SASL: SCRAM-SERVER-FIRST-MESSAGE: iteration missing')\n} else if (!/^[1-9][0-9]*$/.test(iterationText)) {\n  throw new Error('SASL: SCRAM-SERVER-FIRST-MESSAGE: invalid iteration count')\n}\nconst iteration = parseInt(iterationText, 10)\n```\n\nThe regex only validates that the iteration count is a positive integer. There is no minimum bound check.\n\n## Threat model\n\nThis is a **rogue server** scenario. If a client connects to a malicious PostgreSQL server, the server controls the SCRAM `ServerFirstMessage` including the iteration count. By setting `i=1`, the server receives the client's SCRAM proof computed with only 1 PBKDF2 iteration. An attacker who captures this exchange can brute-force the password offline at effectively plaintext speed.\n\nRFC 7677 (SCRAM-SHA-256) Section 4 states:\n\u003e the minimum iteration count SHOULD be at least 4096\n\n## Steps to reproduce\n\n1. Set up a mock PostgreSQL server that responds to SCRAM-SHA-256 with `r=\u003cnonce\u003e,s=\u003csalt\u003e,i=1`\n2. Connect a `pg` client with a password\n3. The client completes the SCRAM exchange using only 1 PBKDF2 iteration\n4. The attacker now has a proof derived with 1 iteration — offline brute-force is trivial\n\n## Impact\n\nPassword compromise via offline brute-force after a single observed authentication exchange with a rogue server.\n\n## Suggested fix\n\nEnforce a minimum iteration count in `parseServerFirstMessage()`:\n\n```js\nconst iteration = parseInt(iterationText, 10)\nif (iteration \u003c 4096) {\n  throw new Error('SASL: SCRAM-SERVER-FIRST-MESSAGE: iteration count ' + iteration + ' is below minimum 4096')\n}\n```","author":{"url":"https://github.com/eddieran","@type":"Person","name":"eddieran"},"datePublished":"2026-04-13T09:19:15.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/3655/node-postgres/issues/3655"}