Merge #1080: Security advisories fixed in version 26

8348000 Add advisory for header announcer block stalling (Greg Sanders)

Pull request description:

  There was one security vulnerability in 25.0 (and below) fixed in 26 (and 25.1). Thanks to Greg Sanders for writing up the advisory.

  This is the last batch of historical disclosures. From now on we'll publicly disclose reported disclosures as per the policy.

ACKs for top commit:
  instagibbs:
    ACK 8348000
  fanquake:
    ACK 8348000
  dergoegge:
    ACK 8348000

Tree-SHA512: 48253477c89b09af4c36a6a7c6ec6871f74abd9d38ff157c3426c03913e18235ef6ac7350f502210ef0d99c4457854a9c7031e3fc643905e20faffadaf0f6cd5

Author: fanquake

_posts/en/posts/2024-11-05-cb-stall-hindering-propagation.md

@@ -0,0 +1,64 @@
+---
+title: Disclosure of hindered block propagation due to stalling peers
+name: blog-disclose-stalling-peers-hindering-propagation
+id: en-blog-disclose-stalling-peers-hindering-propagation
+lang: en
+type: advisory
+layout: post
+
+## If this is a new post, reset this counter to 1.
+version: 1
+
+## Only true if release announcement or security announcement. English posts only
+announcement: 1
+
+excerpt: >
+    A peer could hinder block propagation by announcing blocks first and then simply withholding the block.
+---
+
+Before Bitcoin Core v25.1, an attacker can cause a node to not
+download the latest block.
+
+This issue is considered **Medium** severity.
+
+## Details
+
+When receiving a new block announcement via a headers or compact
+blocks message, the delivering peer is requested either the full
+block or missing transaction details by the receiving node. If
+the announcing peer then doesn't respond as the peer to peer
+protocol requires, the affected Bitcoin Core node will wait
+up to 10 minutes before disconnecting the peer and making another
+block download attempt. If the attacker is able to
+make multiple incoming or outgoing connections, this process
+can be repeated.
+
+Delaying block delivery can cause network degradation by slowing down network convergence,
+making mining payouts less fair, and causing liveliness issues.
+
+This issue was further exacerbated by other issues disclosed recently (for
+instance the [inventory build-up](https://bitcoincore.org/en/2024/10/08/disclose-large-inv-to-send/)),
+when mempools were relatively heterogeneous, disallowing
+opportunistic reconstruction of compact blocks by honest peers.
+
+A mitigation was introduced in [#27626](https://github.com/bitcoin/bitcoin/pull/27626),
+introduced in Bitcoin Core v26.0 and backported to v25.1.
+It ensures that blocks can be requested concurrently from up to 3
+high-bandwidth compact block peers, one of which is required
+to be an outbound connection.
+
+## Attribution
+
+Reported and fixed by Greg Sanders.
+
+## Timeline
+
+- 2023-05-08 - Users reporting block timeouts in the [#bitcoin-core-dev IRC channel](https://bitcoin-irc.chaincode.com/bitcoin-core-dev/2023-05-08)
+- 2023-05-09 - First github issues describing the issue https://github.com/bitcoin/bitcoin/issues/25258#issuecomment-1540028533
+- 2023-05-11 - Mitigation PR opened https://github.com/bitcoin/bitcoin/pull/27626
+- 2023-05-24 - PR merged prior to Bitcoin Core v26.0
+- 2023-05-25 - Backport to Bitcoin Core v25.1 merged https://github.com/bitcoin/bitcoin/pull/27752
+- 2023-10-19 - Bitcoin Core v25.1 Released
+- 2024-11-05 - Public disclosure
+
+{% include references.md %}