Vulnerability-Lookup

CVE-2026-52735 (GCVE-0-2026-52735)

Vulnerability from cvelistv5 – Published: 2026-08-18 19:23 – Updated: 2026-08-18 19:48

Title

ZEBRA: Consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser

Summary

ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, Zebra can accept a block that zcashd rejects because the P2SH signature-operation counter undercounts redeem scripts containing a disabled opcode followed by signature opcodes. In zebra-script/src/lib.rs, p2sh_input_sigop_count used the pure-Rust script::Code::sig_op_count path, whose try_fold parser stops at disabled opcodes such as OP_CODESEPARATOR and returns only the partial count accumulated before the error. The zcashd reference implementation continues static signature-operation counting through disabled opcodes, so an attacker can broadcast P2SH spends that Zebra counts below MAX_BLOCK_SIGOPS while zcashd counts above the 20,000-operation limit. If a Zebra miner includes those transactions, Zebra validators accept the block while zcashd validators reject it, creating a consensus chain split that affects network integrity and availability without requiring the attacker to produce a block. This issue is fixed in version 4.5.0.

Severity

9.3 (Critical)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-18 19:48 UTC

CWE

CWE-684 - Incorrect Provision of Specified Functionality

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/ZcashFoundation/zebra/security…	x_refsource_CONFIRM
https://github.com/ZcashFoundation/zebra/commit/1…	x_refsource_MISC
https://github.com/ZcashFoundation/zebra/releases…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
ZcashFoundation	zebra	Affected: < 4.5.0	guessed

Show details on NVD website

JSON

To clipboard

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}

FKIE_CVE-2026-52735

Vulnerability from fkie_nvd - Published: 2026-08-18 20:17 - Updated: 2026-09-09 21:13

Severity

9.3 (Critical) - CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/ZcashFoundation/zebra/commit/1440b43ca7df59aca948090d45117557b217a6cd
	security-advisories@github.com	https://github.com/ZcashFoundation/zebra/releases/tag/v4.5.0
	security-advisories@github.com	https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-gf9r-m956-97qx

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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      "affectedData": [
        {
          "product": "zebra",
          "vendor": "ZcashFoundation",
          "versions": [
            {
              "status": "affected",
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            }
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    }
  ],
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  "lastModified": "2026-09-09T21:13:25.910",
  "metrics": {
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}

GHSA-GF9R-M956-97QX

Vulnerability from github – Published: 2026-07-02 19:43 – Updated: 2026-07-02 19:43

Summary

zebrad has consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser

Details

Am I affected

You are affected if:

You run any version of zebrad up to and including v4.4.1.
Your node validates blocks on mainnet, testnet, or any network where both Zebra and zcashd nodes participate.

All default configurations are affected. No feature flags, non-default settings, or special build options are required.

Summary

Zebra's P2SH sigop counter uses a pure-Rust code path that short-circuits on disabled opcodes (such as OP_CODESEPARATOR), returning a partial count of zero for any sigops following the disabled opcode. The reference implementation (zcashd) correctly counts through disabled opcodes in its static sigop analysis. This produces a consensus divergence: Zebra accepts blocks that zcashd rejects when the block-wide MAX_BLOCK_SIGOPS = 20,000 threshold is crossed on one side but not the other.

An attacker can exploit this without mining capability. Broadcasting transactions that spend P2SH outputs with malicious redeem scripts is sufficient; any Zebra miner who includes those transactions in a block triggers a chain split between Zebra and zcashd validators.

Details

The P2SH sigop counter at zebra-script/src/lib.rs:399 calls script::Code(redeemed_bytes).sig_op_count(true), which is a pure-Rust path through zcash_script-0.4.4. The legacy (non-P2SH) sigop counter at lib.rs:282-289 correctly uses the C++ FFI via interpreter.legacy_sigop_count_script(). Only the P2SH path bypasses the FFI.

The Rust parser in zcash_script-0.4.4/src/opcode/mod.rs:1247-1260 treats 16 disabled opcodes (0x7e through 0xab, including OP_CAT, OP_SUBSTR, OP_AND, OP_OR, OP_XOR, OP_2MUL, OP_2DIV, OP_MUL, OP_DIV, OP_MOD, OP_LSHIFT, OP_RSHIFT, and OP_CODESEPARATOR) as Err(Error::Disabled(...)). The sig_op_count function at iter.rs:104-115 uses try_fold, which terminates on the first Err and returns the partial sum accumulated so far.

zcashd's GetOp2 (script.h:514-562) returns true for all non-push opcodes including the disabled range. Its GetSigOpCount(true) (script.cpp:152-174) continues counting through disabled opcodes. zcashd rejects disabled opcodes at execution time in the interpreter, not during static sigop analysis.

A redeem script of [0xab, OP_CHECKMULTISIG x 50] produces: Zebra = 0 sigops, zcashd = 1,000 sigops. Across 21 inputs in a block, Zebra computes 0 while zcashd computes 21,000, crossing the MAX_BLOCK_SIGOPS = 20,000 threshold on one side only.

Patches

Patched in Zebra 4.4.2. The fix routes the P2SH sigop counter through the same C++ FFI already used by the legacy sigop counter.

Workarounds

There is no configuration-level workaround. All Zebra nodes validating blocks on a network shared with zcashd are affected. Upgrade as soon as the patched version is available.

Impact

A chain split between Zebra and zcashd validators. The attacker broadcasts spending transactions referencing P2SH outputs whose redeem scripts contain a disabled opcode followed by OP_CHECKSIG or OP_CHECKMULTISIG opcodes. When a Zebra miner (estimated ~30% of current network hashrate) includes these transactions in a block, Zebra validators accept the block while zcashd validators reject it with bad-blk-sigops. The two halves of the network diverge and every subsequent block extending the Zebra-side tip inherits the divergence.

The attacker does not need mining capability, RPC access, or any special privileges. The cost is the transaction fees for the funding and spending transactions.

Credit

Reported by @samsulselfut via a private GitHub Security Advisory submission.

Severity

9.3 (Critical)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.0.1"
      },
      "package": {
        "ecosystem": "crates.io",
        "name": "zebra-script"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.4.1"
      },
      "package": {
        "ecosystem": "crates.io",
        "name": "zebrad"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.5.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-52735"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-684"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-02T19:43:36Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Am I affected\n\nYou are affected if:\n\n1. You run any version of `zebrad` up to and including `v4.4.1`.\n2. Your node validates blocks on mainnet, testnet, or any network where both Zebra and zcashd nodes participate.\n\nAll default configurations are affected. No feature flags, non-default settings, or special build options are required.\n\n### Summary\n\nZebra\u0027s P2SH sigop counter uses a pure-Rust code path that short-circuits on disabled opcodes (such as `OP_CODESEPARATOR`), returning a partial count of zero for any sigops following the disabled opcode. The reference implementation (zcashd) correctly counts through disabled opcodes in its static sigop analysis. This produces a consensus divergence: Zebra accepts blocks that zcashd rejects when the block-wide `MAX_BLOCK_SIGOPS = 20,000` threshold is crossed on one side but not the other.\n\nAn attacker can exploit this without mining capability. Broadcasting transactions that spend P2SH outputs with malicious redeem scripts is sufficient; any Zebra miner who includes those transactions in a block triggers a chain split between Zebra and zcashd validators.\n\n### Details\n\nThe P2SH sigop counter at `zebra-script/src/lib.rs:399` calls `script::Code(redeemed_bytes).sig_op_count(true)`, which is a pure-Rust path through `zcash_script-0.4.4`. The legacy (non-P2SH) sigop counter at `lib.rs:282-289` correctly uses the C++ FFI via `interpreter.legacy_sigop_count_script()`. Only the P2SH path bypasses the FFI.\n\nThe Rust parser in `zcash_script-0.4.4/src/opcode/mod.rs:1247-1260` treats 16 disabled opcodes (0x7e through 0xab, including `OP_CAT`, `OP_SUBSTR`, `OP_AND`, `OP_OR`, `OP_XOR`, `OP_2MUL`, `OP_2DIV`, `OP_MUL`, `OP_DIV`, `OP_MOD`, `OP_LSHIFT`, `OP_RSHIFT`, and `OP_CODESEPARATOR`) as `Err(Error::Disabled(...))`. The `sig_op_count` function at `iter.rs:104-115` uses `try_fold`, which terminates on the first `Err` and returns the partial sum accumulated so far.\n\nzcashd\u0027s `GetOp2` (`script.h:514-562`) returns `true` for all non-push opcodes including the disabled range. Its `GetSigOpCount(true)` (`script.cpp:152-174`) continues counting through disabled opcodes. zcashd rejects disabled opcodes at execution time in the interpreter, not during static sigop analysis.\n\nA redeem script of `[0xab, OP_CHECKMULTISIG x 50]` produces: Zebra = 0 sigops, zcashd = 1,000 sigops. Across 21 inputs in a block, Zebra computes 0 while zcashd computes 21,000, crossing the `MAX_BLOCK_SIGOPS = 20,000` threshold on one side only.\n\n### Patches\n\nPatched in Zebra 4.4.2. The fix routes the P2SH sigop counter through the same C++ FFI already used by the legacy sigop counter.\n\n### Workarounds\n\nThere is no configuration-level workaround. All Zebra nodes validating blocks on a network shared with zcashd are affected. Upgrade as soon as the patched version is available.\n\n### Impact\n\nA chain split between Zebra and zcashd validators. The attacker broadcasts spending transactions referencing P2SH outputs whose redeem scripts contain a disabled opcode followed by `OP_CHECKSIG` or `OP_CHECKMULTISIG` opcodes. When a Zebra miner (estimated ~30% of current network hashrate) includes these transactions in a block, Zebra validators accept the block while zcashd validators reject it with `bad-blk-sigops`. The two halves of the network diverge and every subsequent block extending the Zebra-side tip inherits the divergence.\n\nThe attacker does not need mining capability, RPC access, or any special privileges. The cost is the transaction fees for the funding and spending transactions.\n\n### Credit\n\nReported by `@samsulselfut` via a private GitHub Security Advisory submission.",
  "id": "GHSA-gf9r-m956-97qx",
  "modified": "2026-07-02T19:43:36Z",
  "published": "2026-07-02T19:43:36Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-gf9r-m956-97qx"
    },
    {
      "type": "WEB",
      "url": "https://github.com/AlfredoG87/zcash_script/blob/v0.4.4/src/script/iter.rs#L104-L115"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/ZcashFoundation/zebra"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/zebra-consensus/src/block.rs#L140"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ZcashFoundation/zebra/blob/d4cd662c716382f6397d2a730148025a1ca79fec/zebra-script/src/lib.rs#L383-L400"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "zebrad has consensus divergence via P2SH sigop undercount in pure-Rust disabled-opcode parser"
}

Sightings

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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Action not permitted

CVE-2026-52735 (GCVE-0-2026-52735)

FKIE_CVE-2026-52735

GHSA-GF9R-M956-97QX

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