CloudFlare Quiche

Quiche 0.29.2: UAF via Connection ID Iterator FFI
CVE-2026-11941 5.6 - Medium - June 19, 2026

Cloudflare Quiche was affected by 2 use-after-free vulnerabilities in the connection ID iterator FFI functions. The quiche_connection_id_iter_next and quiche_conn_retired_scid_next functions would return a pointer to a ConnectionId to the applications via function arguments, but the owned ConnectionId would be dropped at the end of those functions' scope. Only applications using those FFI functions are affected. The FFI API is disabled by default by a build-time feature flag. Impact If unpatched, an application calling the affected FFI functions will dereference freed memory. The most likely outcome is undefined behavior leading to a process crash (denial of service). Depending on allocator state, the read may also return adjacent heap contents, resulting in limited information disclosure or incorrect connection identifier handling. Mitigation Users are requested to upgrade to quiche 0.29.2 which is the earliest version containing the fix for this issue.

Dangling pointer

DoS via Infinite Loop in quiche 0.15.0-0.24.4 – RETIRE_CONNECTION_ID
CVE-2025-7054 6.5 - Medium - August 07, 2025

Cloudflare quiche was discovered to be vulnerable to an infinite loop when sending packets containing RETIRE_CONNECTION_ID frames. QUIC connections possess a set of connection identifiers (IDs); see Section 5.1 of RFC 9000 https://datatracker.ietf.org/doc/html/rfc9000#section-5.1 . Once the QUIC handshake completes, a local endpoint is responsible for issuing and retiring Connection IDs that are used by the remote peer to populate the Destination Connection ID field in packets sent from remote to local. Each Connection ID has a sequence number to ensure synchronization between peers. An unauthenticated remote attacker can exploit this vulnerability by first completing a handshake and then sending a specially-crafted set of frames that trigger a connection ID retirement in the victim. When the victim attempts to send a packet containing RETIRE_CONNECTION_ID frames, Section 19.16 of RFC 9000 https://datatracker.ietf.org/doc/html/rfc9000#section-19.6 requires that the sequence number of the retired connection ID must not be the same as the sequence number of the connection ID used by the packet. In other words, a packet cannot contain a frame that retires itself. In scenarios such as path migration, it is possible for there to be multiple active paths with different active connection IDs that could be used to retire each other. The exploit triggered an unintentional behaviour of a quiche design feature that supports retirement across paths while maintaining full connection ID synchronization, leading to an infinite loop.This issue affects quiche: from 0.15.0 before 0.24.5.

Cloudflare quiche <0.24.4: Congestion Window Overgrowth & Overflow
CVE-2025-4821 - June 18, 2025

Impact Cloudflare quiche was discovered to be vulnerable to incorrect congestion window growth, which could cause it to send data at a rate faster than the path might actually support. An unauthenticated remote attacker can exploit the vulnerability by first completing a handshake and initiating a congestion-controlled data transfer towards itself. Then, it could manipulate the victim's congestion control state by sending ACK frames covering a large range of packet numbers (including packet numbers that had never been sent); see RFC 9000 Section 19.3. The victim could grow the congestion window beyond typical expectations and allow more bytes in flight than the path might really support. In extreme cases, the window might grow beyond the limit of the internal variable's type, leading to an overflow panic. Patches quiche 0.24.4 is the earliest version containing the fix for this issue.

Cloudflare Quiche 0.24.4 Congestion Window Attack Vulnerability
CVE-2025-4820 - June 18, 2025

Impact Cloudflare quiche was discovered to be vulnerable to incorrect congestion window growth, which could cause it to send data at a rate faster than the path might actually support. An unauthenticated remote attacker can exploit the vulnerability by first completing a handshake and initiating a congestion-controlled data transfer towards itself. Then, it could manipulate the victim's congestion control state by sending ACK frames exercising an opportunistic ACK attack; see RFC 9000 Section 21.4. The victim could grow the congestion window beyond typical expectations and allow more bytes in flight than the path might really support. Patches quiche 0.24.4 is the earliest version containing the fix for this issue.

Cloudflare Quiche <=0.19.1/0.20.0 Unlimited Resource Allocation Vulnerability
CVE-2024-1765 7.5 - High - March 12, 2024

Cloudflare Quiche (through version 0.19.1/0.20.0) was affected by an unlimited resource allocation vulnerability causing rapid increase of memory usage of the system running quiche server or client. A remote attacker could take advantage of this vulnerability by repeatedly sending an unlimited number of 1-RTT CRYPTO frames after previously completing the QUIC handshake. Exploitation was possible for the duration of the connection which could be extended by the attacker.  quiche 0.19.2 and 0.20.1 are the earliest versions containing the fix for this issue.

Allocation of Resources Without Limits or Throttling

Cloudflare Quiche <0.20.1 unbounded C_ID queue exploitation
CVE-2024-1410 5.3 - Medium - March 12, 2024

Cloudflare quiche was discovered to be vulnerable to unbounded storage of information related to connection ID retirement, which could lead to excessive resource consumption. Each QUIC connection possesses a set of connection Identifiers (IDs); see RFC 9000 Section 5.1 https://datatracker.ietf.org/doc/html/rfc9000#section-5.1 . Endpoints declare the number of active connection IDs they are willing to support using the active_connection_id_limit transport parameter. The peer can create new IDs using a NEW_CONNECTION_ID frame but must stay within the active ID limit. This is done by retirement of old IDs, the endpoint sends NEW_CONNECTION_ID includes a value in the retire_prior_to field, which elicits a RETIRE_CONNECTION_ID frame as confirmation. An unauthenticated remote attacker can exploit the vulnerability by sending NEW_CONNECTION_ID frames and manipulating the connection (e.g. by restricting the peer's congestion window size) so that RETIRE_CONNECTION_ID frames can only be sent at a slower rate than they are received, leading to storage of information related to connection IDs in an unbounded queue. Quiche versions 0.19.2 and 0.20.1 are the earliest to address this problem. There is no workaround for affected versions.

Unbounded Path Validation Queuing in Quiche <0.19.0 (CVE-2023-6193)
CVE-2023-6193 5.3 - Medium - December 12, 2023

quiche v. 0.15.0 through 0.19.0 was discovered to be vulnerable to unbounded queuing of path validation messages, which could lead to excessive resource consumption. QUIC path validation (RFC 9000 Section 8.2) requires that the recipient of a PATH_CHALLENGE frame responds by sending a PATH_RESPONSE. An unauthenticated remote attacker can exploit the vulnerability by sending PATH_CHALLENGE frames and manipulating the connection (e.g. by restricting the peer's congestion window size) so that PATH_RESPONSE frames can only be sent at the slower rate than they are received; leading to storage of path validation data in an unbounded queue. Quiche versions greater than 0.19.0 address this problem.

Resource Exhaustion