Bump seed canonicalization is a critical security practice in Solana program development. When deriving a Program Derived Address (PDA), the runtime searches for a "bump" value (starting from 255 and decrementing) that produces an address off the Ed25519 curve. The canonical bump is the first valid value found (the highest valid bump). Using any other valid bump for the same seeds would produce a different address, creating a vulnerability.

The vulnerability

The Pubkey::find_program_address function always returns the canonical bump (highest valid bump). However, if a program uses Pubkey::create_program_address and accepts a user-supplied bump without verifying it is the canonical one, multiple valid PDAs can exist for the same logical seed set.

An attacker can exploit this by:

1. Discovering a non-canonical bump that also produces a valid PDA
2. Initializing a duplicate account at the non-canonical address
3. Using this duplicate to bypass uniqueness assumptions in the program's logic

Mitigation

With the Anchor framework: The seeds and bump constraints automatically enforce canonical bump usage:

1#[account(
2    seeds = [b"vault", user.key().as_ref()],
3    bump  // Anchor verifies the canonical bump
4)]
5pub vault: Account<'info, Vault>,

In native programs: Store the canonical bump during account initialization and validate it on every subsequent access:

1// During initialization
2let (pda, canonical_bump) = Pubkey::find_program_address(seeds, program_id);
3account_data.bump = canonical_bump;
4
5// During subsequent access
6let expected_pda = Pubkey::create_program_address(
7    &[seeds, &[account_data.bump]],
8    program_id,
9)?;
10assert_eq!(expected_pda, account_info.key());

Audit checklist

When auditing for bump seed canonicalization issues, security researchers should:

• Verify that find_program_address (not create_program_address) is used during initialization
• Confirm the canonical bump is stored in the account data
• Check that subsequent accesses validate the stored bump
• Ensure Anchor programs use the bump constraint on all PDA accounts

Bump seed canonicalization is one of the most common sources of high-severity vulnerabilities in Solana programs and is a mandatory check in any security audit.