ZEBRA: Unbounded memory leak in mempool download pipeline via timeout path cancel_handles retention

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ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, an unauthenticated P2P peer can cause the mempool download pipeline to retain transactions after verification reaches the outer RATE_LIMIT_DELAY timeout. In zebrad/src/components/mempool/downloads.rs, Downloads::poll_next removed cancel_handles entries after success and ordinary verification errors, but tokio::time::error::Elapsed did not carry the UnminedTxId needed to remove the timed-out entry. Each retained cancel_handles entry could hold a full Gossip::Tx(UnminedTx), while normal mined-transaction cleanup could not match attacker transactions and no periodic garbage collection or count cap existed. Sustained traffic therefore caused monotonic memory growth until swap pressure degraded the node or the operating system terminated the zebrad process for exhausting memory. This issue is fixed in version 4.5.0.

Source published

18 Aug 2026 19:19:56 UTC

Source modified

19 Aug 2026 18:20:44 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 4.5.0, an unauthenticated P2P peer can cause the mempool download pipeline to retain transactions after verification reaches the outer RATE_LIMIT_DELAY timeout. In zebrad/src/components/mempool/downloads.rs, Downloads::poll_next removed cancel_handles entries after success and ordinary verification errors, but tokio::time::error::Elapsed did not carry the UnminedTxId needed to remove the timed-out entry. Each retained cancel_handles entry could hold a full Gossip::Tx(UnminedTx), while normal mined-transaction cleanup could not match attacker transactions and no periodic garbage collection or count cap existed. Sustained traffic therefore caused monotonic memory growth until swap pressure degraded the node or the operating system terminated the zebrad process for exhausting memory. This issue is fixed in version 4.5.0.

Source published

Aug 18, 2026, 7:19:56 PM (timezone not stated)

Source modified

Aug 19, 2026, 6:20:44 PM (timezone not stated)

Observed here

7 Nov 2026 11:35:36 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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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 4.5.0, an unauthenticated P2P peer can cause the mempool download pipeline to retain transactions after verification reaches the outer RATE_LIMIT_DELAY timeout. In zebrad/src/components/mempool/downloads.rs, Downloads::poll_next removed cancel_handles entries after success and ordinary verification errors, but tokio::time::error::Elapsed did not carry the UnminedTxId needed to remove the timed-out entry. Each retained cancel_handles entry could hold a full Gossip::Tx(UnminedTx), while normal mined-transaction cleanup could not match attacker transactions and no periodic garbage collection or count cap existed. Sustained traffic therefore caused monotonic memory growth until swap pressure degraded the node or the operating system terminated the zebrad process for exhausting memory. This issue is fixed in version 4.5.0.

Source published

18 Aug 2026 20:17:17 UTC

Source modified

22 Oct 2026 22:10:00 UTC

Observed here

25 Oct 2026 13:17:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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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: 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

### Am I affected You are affected if: 1. You run `zebrad` up to and including `v4.4.1`. 2. Your node accepts inbound P2P connections (`network.listen_addr` is set, which is the default). 3. Your node's mempool is active (node is synced near the chain tip). All default configurations are affected. ### Summary The mempool download pipeline's `cancel_handles` map retains entries for transactions whose verification times out at the outer `RATE_LIMIT_DELAY` (73-second) boundary. The `tokio::time::error::Elapsed` error carries no payload, so the transaction ID is unrecoverable and the corresponding `cancel_handles` entry (including the full `Gossip::Tx(UnminedTx)`, up to ~2 MB) is never removed. Entries accumulate monotonically with no upper bound or garbage collection, leading to eventual out-of-memory process termination. ### Details `Downloads::poll_next()` at `zebrad/src/components/mempool/downloads.rs:215-228` handles three terminal states for a verification task: - `Ok(Ok(...))`: success. Calls `cancel_handles.remove(&tx.transaction.id)`. Correct. - `Ok(Err(...))`: verification error. Calls `cancel_handles.remove(&hash)`. Correct. - `Err(elapsed)`: outer timeout. Returns `Err(elapsed)` without removing anything. **Bug.** `tokio::time::error::Elapsed` has no payload, so the timed-out transaction's `UnminedTxId` is unrecoverable from the error. The consumer at `zebrad/src/components/mempool.rs:663-672` explicitly acknowledges this gap with a TODO comment. The only cleanup paths for `cancel_handles` are `cancel(mined_ids)` (removes entries matching mined transaction IDs; attacker transactions are never mined) and `cancel_all()` (clears everything on shutdown or chain reset). No periodic GC, no time-based eviction, and no count cap exists. For direct `tx` pushes (`Gossip::Tx`), the retained entry holds the full deserialized transaction, which can be up to ~9 MB in memory for a transaction near the transparent-output extreme. Per-connection leak rate at worst case: ~685 KB/s (~2.4 GB/hour). ### Patches The fix preserves the `UnminedTxId` through the timeout error path: wrap the timeout future so the spawned task's outer error carries the txid (e.g., `Err((txid, elapsed))`). In `Downloads::poll_next()`, on the timeout arm, call `cancel_handles.remove(&txid)`. ### Workarounds There is no configuration-level workaround. Restarting the node clears the accumulated entries. Operators running in memory-constrained environments (containers with cgroup limits) may see the process killed by the OOM killer before natural recovery. ### Impact Gradual, unbounded memory exhaustion of a Zebra node from unauthenticated P2P traffic. The leak is monotonic (entries are never freed under normal operation) but slow (~685 KB/s per connection worst case). An attacker must sustain traffic for hours to exhaust typical server memory. The node continues operating normally until memory pressure becomes critical, at which point the OS OOM killer terminates the process or the node degrades due to swap pressure. No consensus impact, no fund loss, no on-disk corruption. ### Credit Reported by `@AnticsDecoded` via a private GitHub Security Advisory submission. Working E2E reproduction on a live regtest node with staged parent/child transaction dependencies.

Source published

2 Jul 2026 20:12:35 UTC

Source modified

2 Jul 2026 20:26:31 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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

Publisher rating · MODERATE