CVE-2026-84784 - Vulnerability Details

- QUIC: Unbounded RETIRE_CONNECTION_ID Backlog

Description

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.

Published: 2026-09-29

Score: 7.5 High

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

A remote host can send a large number of NEW_CONNECTION_ID frames to a local OpenSSL QUIC stack, causing the stack to enqueue a RETIRE_CONNECTION_ID frame for each received frame. Because the stack releases these frames only after an ACK is received, an attacker can avoid ACKs and force the Local QUIC stack to allocate up to around 400 MB of memory, leading to resource exhaustion. This issue arises from a flaw in the QUIC implementation that disregards limits on the number of connection identifiers and is classified as CWE‑770: Allocation of Resources Without Limits or Throttling.

Affected Systems

The vulnerability affects the OpenSSL QUIC implementation in all product releases that include QUIC support. Specific affected version ranges are not provided in the advisory, so all releases prior to the fix that contain the QUIC stack are considered vulnerable.

Risk and Exploitability

The CVSS score of 7.5 indicates moderate‑to‑high severity, and although the EPSS score is not available, the lack of a KEV listing suggests exploitation is not yet widely documented. An attacker can trigger the issue from the remote side without special privileges by sending large volumes of QUIC frames and suppressing ACKs. The exploitation requires a reachable QUIC service and the ability to send or replay QUIC frames, implying that the attack vector is remote and unauthenticated.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

OpenSSL

unaffected

Version	Status	Constraints
`4.0.0`	affected	< 4.0.3
`3.6.0`	affected	< 3.6.5
`3.5.0`	affected	< 3.5.9
`3.4.0`	affected	< 3.4.8

Configuration 1 [-]

OR	cpe:2.3:a:openssl:openssl::::::::
	cpe:2.3:a:openssl:openssl::::::::
	cpe:2.3:a:openssl:openssl::::::::
	cpe:2.3:a:openssl:openssl::::::::

No data.

Vendor Product Confidence Versions

Openssl

100%

Version	Status	Scheme	Platform
`[4.0.0,4.0.3)`	affected	semver	—
`[3.6.0,3.6.5)`	affected	semver	—
`[3.5.0,3.5.9)`	affected	semver	—
`[3.4.0,3.4.8)`	affected	semver	—

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Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade OpenSSL to a release that contains the fix for CVE‑2026‑84784.
If an immediate upgrade is not feasible, consider disabling QUIC traffic or configuring a firewall rule to rate‑limit QUIC packets to mitigate resource exhaustion.
Implement monitoring on QUIC connection buffers and trigger an automated restart or resource cleanup when the buffer size exceeds a safe threshold.

Generated by OpenCVE AI on September 29, 2026 at 22:30 UTC.

Tracking

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Advisories

Source	ID	Title
Debian DSA	DSA-6531-1	openssl security update
Ubuntu USN	USN-8847-1	OpenSSL vulnerabilities

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00607.

Exploitation none

Automatable yes

Technical Impact partial

References

Link	Providers
https://github.com/openssl/openssl/commit/4685c914b0d410b1034f40b547c95bc95e7a380a
https://github.com/openssl/openssl/commit/9a30fe0fba195c14e5b87bf93c0d0fdb70373806
https://github.com/openssl/openssl/commit/dba3c48d653c64fcbc9070a17a0ee2b3e2f3af1f
https://github.com/openssl/openssl/commit/e9e5155833fa968bee50024bf9ca3a185ab599fe
https://nvd.nist.gov/vuln/detail/CVE-2026-84784
https://openssl-library.org/news/secadv/20260929.txt
https://www.cve.org/CVERecord?id=CVE-2026-84784

History

Thu, 08 Oct 2026 01:30:00 +0000

Type	Values Removed	Values Added
CPEs		cpe:2.3:a:openssl:openssl::::::::

Wed, 30 Sep 2026 00:15:00 +0000

Type	Values Removed	Values Added
References		https://nvd.nist.gov/vuln/detail/CVE-2026-84784 https://www.cve.org/CVERecord?id=CVE-2026-84784
Metrics	threat_severity `None`	threat_severity `Moderate`

Tue, 29 Sep 2026 17:45:00 +0000

Type	Values Removed	Values Added
First Time appeared		Openssl Openssl openssl
Vendors & Products		Openssl Openssl openssl

Tue, 29 Sep 2026 17:30:00 +0000

Type	Values Removed	Values Added
Metrics		cvssV3_1 `{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}` ssvc `{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Tue, 29 Sep 2026 15:45:00 +0000

Type	Values Removed	Values Added
Description		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.
Title		QUIC: Unbounded RETIRE_CONNECTION_ID Backlog
Weaknesses		CWE-770
References		https://github.com/openssl/openssl/commit/4685c914b0d410b1034f40b547c95bc95e7a380a https://github.com/openssl/openssl/commit/9a30fe0fba195c14e5b87bf93c0d0fdb70373806 https://github.com/openssl/openssl/commit/dba3c48d653c64fcbc9070a17a0ee2b3e2f3af1f https://github.com/openssl/openssl/commit/e9e5155833fa968bee50024bf9ca3a185ab599fe https://openssl-library.org/news/secadv/20260929.txt

Subscriptions

Openssl Openssl

MITRE

Status: PUBLISHED

Assigner: openssl

Published: 2026-09-29T15:32:25.758Z

Updated: 2026-09-29T16:44:09.766Z

Reserved: 2026-09-02T10:14:02.262Z

Link: CVE-2026-84784

Vulnrichment

Updated: 2026-09-29T16:43:59.933Z

NVD

Status : Analyzed

Published: 2026-09-29T16:17:12.810

Modified: 2026-10-08T01:21:22.543

Link: CVE-2026-84784

Redhat

Severity : Moderate

Publid Date: 2026-09-29T15:32:25Z

Links: CVE-2026-84784 - Bugzilla

OpenCVE Enrichment

Updated: 2026-09-29T22:30:19Z

Weaknesses

CWE-770
Allocation of Resources Without Limits or Throttling

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

Exploitation none

Automatable yes

Technical Impact partial

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