Zebra P2SH Sigop Undercount Vulnerability Causes Network Fork (GHSA-2prc-cj5x-4443)

P2SH Sigop Undercount Not Correctly Fixed Vulnerability Overview Vulnerability ID: GHSA-2prc-cj5x-4443 Severity: Critical Publication Date: Jun 1 Description: Zebra's P2SH sigop counter incorrectly used the legacy sigop counting method ( ) instead of Zcash's accurate sigop counting method ( ). This caused Zebra to overcount the number of sigops in P2SH outputs by a factor of 20 during block validation, potentially triggering block validation failures and resulting in a network fork. Impact Scope Affected Versions: - : 7.0.0 - : 4.5.0 Fixed Versions: - : 7.0.1 - : 4.5.1 Impact Conditions: - Using Zebra version 4.5.0 or later (note: older versions may have other vulnerabilities). - The node is validating blocks on a network where both Zebra and Zcash nodes participate. - Under default configuration, no special flags, non-default settings, or special build options are required. Remediation Patch: In Zebra 4.5.1, the implementation was switched back to Rust, fixing the original discrepancy that led to GHSA-qf9r-m956-97qg. Workarounds: No workaround is available at the configuration level. All Zebra nodes validating blocks on shared networks are affected. It is recommended to upgrade to the patched version as soon as possible. Detailed Information Vulnerability Mechanism: - Zebra's P2SH sigop counter in used , whereas Zcash's accurate sigop counting requires . - This caused Zebra to overcount the number of sigops in P2SH outputs by a factor of 20 during block validation, potentially triggering block validation failures and resulting in a network fork. Attack Scenario: - The attacker does not need mining capabilities; they only need to broadcast a valid P2SH transaction containing a low-threshold multi-signature script. - Once miners include these transactions in a block, Zebra validators will reject the block while other nodes in the network will accept it, causing a network fork. Example: - A block containing 1,001 P2SH outputs, each containing an , will result in 20,020 sigops in Zebra, whereas Zcash will calculate only 1,001 sigops. - This causes Zebra's total sigop count to exceed the threshold of 20,000, while Zcash's will not. References zcash getP2SHSigopCount() and Script::getSigopCount(const CScript&): Reference for the behavior of P2SH counting in accurate mode. zcash Script::getSigopCount(bool fAccurate): The flag controls the accuracy of multi-signature counting.

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Zebra P2SH Sigop Undercount Vulnerability Causes Network Fork (GHSA-2prc-cj5x-4443)

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