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🛡️ CVE-2026-44498 — zebrad

🔴 CVSS 9.5 — Critical ✅ No Known Exploit CWE-682 OSV
9.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Zebra's Block Validator Undercounts Coinbase and P2SH Sigops

Zebra's block validator undercounts transparent signature operations against the 20000-sigop block limit (MAX_BLOCK_SIGOPS), allowing it to accept blocks that zcashd rejects with bad-blk-sigops. A miner who produces such a block can split the network: Zebra nodes follow the offending chain while zcashd nodes do not.

Two distinct undercounts:

A: Coinbase Hidden Legacy Sigops

zcashd's GetLegacySigOpCount() includes the coinbase input's scriptSig. Zebra's Sigops impl skipped the coinbase input entirely, so up to ~98 sigops (the 100-byte coinbase script length cap, less the height prefix) could be hidden inside the coinbase scriptSig without being charged against the block limit.

B: Aggregate P2SH Sigops.

zcashd's GetP2SHSigOpCount() parses each P2SH input's redeem script with accurate=true and sums those sigops into the block-wide total via ConnectBlock. The check is per-block, not per-transaction, and the limit applies regardless of who mines the offending block — a miner just needs to include enough P2SH-spending transactions whose redeem scripts together exceed 20000 sigops. Zebra computed P2SH sigops only on the mempool-acceptance path (used for ZIP-317 weighting) and never accumulated them during block validation. A block whose aggregate redeem-script sigops exceed 20000 (e.g. 1334 P2SH spends × 15 sigops = 20010) would be accepted by Zebra and rejected by zcashd.

Patches

Fixed in this release: https://github.com/ZcashFoundation/zebra/releases/tag/v4.4.0.

Workarounds

None. Operators relying on Zebra for consensus should upgrade.

Resources

  • MAX_BLOCK_SIGOPS constant inherited from Bitcoin via the Zcash protocol spec's §7.6 catch-all "Other rules inherited from Bitcoin", tracked for explicit documentation in [zcash/zips#568](https://github.com/zcash/zips/issues/568).
  • zcashd GetLegacySigOpCount: <https://github.com/zcash/zcash/blob/v6.11.0/src/main.cpp#L826-L836>
  • zcashd GetP2SHSigOpCount: <https://github.com/zcash/zcash/blob/v6.11.0/src/main.cpp#L840-L852>
  • zcashd ConnectBlock aggregates per-tx sigops and compares against MAX_BLOCK_SIGOPS.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity high, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: None — no deployment-specific condition has to hold.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Confidentiality impact: None.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: None.

Weakness class

CVE-2026-44498 is classified as CWE-682: Incorrect Calculation. The product performs a calculation that generates incorrect or unintended results that are later used in security-critical decisions or resource management.

Affected software

CVE-2026-44498 is recorded against 1 package.

  • zebrad

Timeline and source

Published on 7 May 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Package)
github.com (Web)

Other advisories for this package

zebrad has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-682: Incorrect Calculation) in other software:

Details

Severity CRITICAL
CVSS Score 9.5
CVSS Vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N
CWE CWE-682
Public Exploit ✅ No
Source OSV
Published 2026-05-07
Updated 2026-08-20
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
zebrad — —

Similar Threats

Exploit Protection

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