NRDAX-T0182 - Optimistic ACK Congestion Window Manipulation

memory_amp · active · first seen 2026-07-10

provenance: Reproduced in NullRabbit's attack-reproduction pipeline

mechanism

quiche optimistic-ACK congestion-window growth (CVE-2025-4820): a QUIC peer completes a handshake, initiates a congestion-controlled transfer toward itself, then sends ACK frames (type 0x02 / 0x03) ac

instances (2)

chain	primitive	fidelity	origin	reproducer (bundle)	source
quic	quic_optimistic_ack_cwnd_growth	lab	reverse-engineered-cve	quic_optimistic_ack_cwnd_growth	CVE-2025-4820 / GHSA-2v9p-3p3h-w56j — https://github.com/cloudflare/quiche/security/advisories/GHSA-2v9p-3p3h-w56j (see also https://blog.cloudflare.com/defending-quic-from-acknowledgement-based-ddos-attacks/ and RFC 9000 §21.4 Optimistic ACK Attack). cloudflare/quiche < 0.24.4 incorrectly grows its congestion window in response to ACK frames that acknowledge packets the peer never received (optimistic / opportunistic ACK), allowing more bytes in flight than the path supports and transmission faster than the path can handle. Fixed in quiche 0.24.4 (dynamic CWND-aware packet-number skipping so a forward ACK for a not-yet-sent packet number is caught).
quic	quiche_ack_never_sent_cwnd	proxy	reverse-engineered-cve	quiche_ack_never_sent_cwnd	-

related (memory_amp)

NRDAX-T0023 - Coalesced Packet Buffer Leak active NRDAX-T0025 - Compact Block Size Integer Overflow active NRDAX-T0038 - Count Underflow Header Serving Amplification active NRDAX-T0042 - Crypto Frame Reassembly Buffer Exhaustion active NRDAX-T0046 - Decompression Bomb Resource Exhaustion active NRDAX-T0059 - Duplicate Transport Parameter Memory Leak active NRDAX-T0061 - Duplicate Tx Mempool Index Desync active NRDAX-T0071 - Ethash Verification Memory Exhaustion active

cite

https://nrdax.com/techniques/NRDAX-T0182

plain

NRDAX Registry. Technique NRDAX-T0182.

bibtex

@misc{nrdax_NRDAX_T0182,
  title = {Optimistic ACK Congestion Window Manipulation (NRDAX-T0182)},
  howpublished = {NRDAX Registry},
  url = {https://nrdax.com/techniques/NRDAX-T0182},
}

json (csl)

{
  "id": "nrdax-NRDAX-T0182",
  "type": "dataset",
  "title": "Optimistic ACK Congestion Window Manipulation (NRDAX-T0182)",
  "URL": "https://nrdax.com/techniques/NRDAX-T0182",
  "publisher": "NRDAX Registry"
}