ZEBRA: Allocation Amplification in Inbound Network Deserializers

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.4.0, prior to zebra-chain version 7.0.0, and prior to zebra-network version 6.0.0, several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks. This issue has been patched in zebrad version 4.4.0, zebra-chain version 7.0.0, and zebra-network version 6.0.0.

Source published

8 May 2026 15:10:21 UTC

Source modified

8 May 2026 19:41:46 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.4.0, prior to zebra-chain version 7.0.0, and prior to zebra-network version 6.0.0, several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks. This issue has been patched in zebrad version 4.4.0, zebra-chain version 7.0.0, and zebra-network version 6.0.0.

Source published

May 8, 2026, 3:10:21 PM (timezone not stated)

Source modified

May 8, 2026, 7:41:46 PM (timezone not stated)

Observed here

7 Nov 2026 10:31:11 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.4.0, prior to zebra-chain version 7.0.0, and prior to zebra-network version 6.0.0, several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks. This issue has been patched in zebrad version 4.4.0, zebra-chain version 7.0.0, and zebra-network version 6.0.0.

Source published

8 May 2026 15:17:01 UTC

Source modified

26 Oct 2026 18:10:00 UTC

Observed here

27 Oct 2026 11:12:17 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

# CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers ## Summary Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across `headers` messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks. ## Severity **Moderate** - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in. Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant. ## Affected Versions All Zebra versions prior to 4.4.0. ## Description Zebra's network codec uses `TrustedPreallocate` and generic `Vec` deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified: - **`headers` message receive cap.** `read_headers()` deserialized the `CountedHeader` vector via the generic `TrustedPreallocate` path, which allowed up to ~1,409 entries per message. The protocol ceiling `MAX_FIND_BLOCK_HEADERS_RESULTS = 160` was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes. - **Equihash solution length.** `Solution::zcash_deserialize` decoded the solution as a generic `Vec<u8>` and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in `Solution::from_bytes`. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection. - **Sapling spend vectors in coinbase transactions.** V5 `spend_prefixes` and V4 `shielded_spends` were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier. - **Coinbase script bytes.** `Input::zcash_deserialize()` read the coinbase script as a generic `Vec<u8>` up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes. An attacker could exploit this by: - Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake). - Sending one of: a `headers` message with a CompactSize count up to ~1,409, a `block` whose header carries an inflated equihash CompactSize, a `tx` declaring a coinbase input with a large `nSpendsSapling`, or a `block` with a coinbase input whose script length is near the message-size ceiling. - The deserializer allocates against the loose ceiling, parses, and only then rejects. ## Impact **Denial of Service** - **Attack Vector:** Network. - **Effect:** Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available. - **Scope:** Any affected Zebra node. ## Fixed Versions This issue is fixed in Zebra 4.4.0. ## Mitigation Users should upgrade to Zebra 4.4.0 or later immediately. There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages. ## Credits Zebra thanks @Zk-nd3r for finding and reporting the issues.

Source published

7 May 2026 20:55:28 UTC

Source modified

13 May 2026 13:55:12 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Publisher rating · MODERATE