OpenSSL QUIC stack no CID limit check 400MB memory exhaustion
CVE-2026-84784 Published on September 29, 2026
QUIC: Unbounded RETIRE_CONNECTION_ID Backlog
Issue summary: A malicious remote peer may flood the local QUIC
stack with NEW_CONNECTION_ID frames by avoiding a limit check on
how many connection IDs the remote QUIC stack can use.
Impact summary: The local QUIC stack sends a RETIRE_CONN_ID frame
for every NEW_CONNECTION_ID frame it receives. The RETIRE_CONN_ID
frame is dispatched via the Control Frame Queue (CFQ). If the remote
peer also withholds ACKs, then it can force the local stack
to allocate ~400MB (depending on ACK delay).
CWE: CWE-770: Allocation of Resources Without Limits or Throttling
Description: RFC 9000 sections 5.1.1 and 5.1.2 [1] describe the mechanism
by which a remote peer can notify the local QUIC stack to change the
destination connection ID (a.k.a. CID) the local stack uses to
identify the connection at the remote peer. Each CID is associated
with a sequence number. The sequence number is transmitted
in NEW_CONNECTION_ID and RETIRE_CONNECTION_ID frames to identify the CID
which is being either associated with a connection or retired.
The remote peer sends a NEW_CONNECTION_ID frame to let the local stack know
a new CID is being associated with an existing connection. The
NEW_CONNECTION_ID frame carries the new CID, its sequence number, and the
retire-prior-to number. The retire-prior-to identifies existing
CIDs that are to be retired. The local QUIC stack must send a
RETIRE_CONNECTION_ID for every destination CID whose sequence number
is less than retire-prior-to. The CID becomes retired after the
local stack receives an ACK for its RETIRE_CONNECTION_ID frame.
Although the OpenSSL QUIC stack supports at most one destination CID
for every connection, it can be tricked into processing more than
one RETIRE_CONNECTION_ID frame per connection. The OpenSSL QUIC
stack currently retires the destination CID as soon as it receives
the NEW_CONNECTION_ID, while in fact the destination CID must
be retired after an ACK for the RETIRE_CONNECTION_ID frame is received.
Correcting the flawed logic also fixes the backlog growth.
[1] https://datatracker.ietf.org/doc/html/rfc9000#name-issuing-connection-ids
FIPS impact: no
The FIPS module is not affected as the QUIC implementation is outside of
the OpenSSL FIPS module boundary.
Vulnerability Analysis
CVE-2026-84784 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
Allocation of Resources Without Limits or Throttling
The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.
Products Associated with CVE-2026-84784
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Affected Versions
OpenSSL:- Version 4.0.0 and below 4.0.3 is affected.
- Version 3.6.0 and below 3.6.5 is affected.
- Version 3.5.0 and below 3.5.9 is affected.
- Version 3.4.0 and below 3.4.8 is affected.