-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

0xCERT Security Advisory 0xCERT-2026-0300
============================================================

Advisory-ID:  0xCERT-2026-0300
Severity:     Medium
Published:    2026-11-02T10:46:00.000Z
Updated:      2026-11-02T12:44:06.945Z
Chains:       Ethereum
URL:          https://www.0xcert.com/advisory/0xCERT-2026-0300

Title: Besu 26.11.0 upgrades Vert.x to 5.2.2 to fix October 2026 Vert.x advisories, including HTTP/1.x request smuggling

Summary
- -------
Besu 26.11.0 upgrades Vert.x from 5.1.6 to 5.2.2, fixing the Vert.x advisories published in October 2026 (HTTP/1.x request smuggling, unbounded allocation for compressed WebSocket frames, incomplete HTTP client SSL context cache key). Operators should upgrade.

Details
- -------
Summary
Besu 26.11.0 (released 2026-11-02) upgrades its Vert.x dependency from 5.1.6 to 5.2.2, which per the release notes fixes the Vert.x advisories published in October 2026 (#11770). The release also changes some defaults and RPC behaviour.

Affected
- - Besu (hyperledger/besu, now besu-eth/besu) versions before 26.11.0 bundling Vert.x 5.1.6
- - Fixed in 26.11.0

Impact
The release notes name the fixed Vert.x issue types as HTTP/1.x request smuggling, unbounded allocation for compressed WebSocket frames, and an incomplete HTTP client SSL context cache key. No CVE/GHSA identifiers are given in the notes and no exploitation in the wild is reported.

Recommended actions
- - Upgrade Besu to 26.11.0 or later
- - Review breaking changes: --Xpos-block-finalization-timeout-ms default changes from 800 to 0 (#11774); eth_getProof follows execution-apis leading-zero/error rules (#11668); eth_simulateV1 rejects unknown account overrides (#11695)
- - Avoid exposing JSON-RPC/WebSocket endpoints to untrusted networks

Source & attribution
This 0xCERT advisory relays the Besu 26.11.0 release notes: https://github.com/besu-eth/besu/releases/tag/26.11.0. Details may change; refer to the upstream project for the authoritative record and any follow-up security advisories.

References
- ----------
- - https://github.com/besu-eth/besu/releases/tag/26.11.0

Verify with the 0xCERT OpenPGP key: https://www.0xcert.com/pgp.asc
Fingerprint: 5F94 3ED1 1E50 CF31 2128  C493 CCC7 D9EC 9415 723D

-----BEGIN PGP SIGNATURE-----

wrsEARYKAG0Fgmro+jcJEDe9Tbcr+ZxrRRQAAAAAABwAIHNhbHRAbm90YXRp
b25zLm9wZW5wZ3Bqcy5vcmdeUhFa8OJ5VPQG5pklqI2pCtZB612dFt+DshSF
pberMxYhBGCkkFZbJcT5QWu27ze9Tbcr+ZxrAAACYgD+J3rQN8J1x3SgcJ8T
yRFil+ME8PCePUoOVrXOr2HvK7EA/1IwfUEfGnHuPiLIByvicXRknGmjWvk3
RxGTexAPIMQH
=ysIf
-----END PGP SIGNATURE-----