CVE-2021-24029Network attack vector

Unauthenticated server crash via duplicate write cipher

Published Mar 15, 2021 · Updated Aug 3, 2024

Reachable assertion in affected Meta mvfst and Proxygen releases allows remote attackers to crash QUIC servers with a crafted handshake. In updateHandshakeState, duplicated ClientHello and ClientFinished processing derives a second 1-RTT write cipher, and the existing CHECK aborts the process instead of returning a QUIC connection error. An unauthenticated network peer must reach a server using the affected QUIC transport; the failure terminates the hosting process rather than only rejecting that connection.

CVSS severity7.5
High
EPSS probability1.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in affected Meta mvfst and Proxygen releases allows remote attackers to crash QUIC servers with a crafted handshake. In updateHandshakeState, duplicated ClientHello and ClientFinished processing derives a second 1-RTT write cipher, and the existing CHECK aborts the process instead of returning a QUIC connection error. An unauthenticated network peer must reach a server using the affected QUIC transport; the failure terminates the hosting process rather than only rejecting that connection.

The record

CVE
CVE-2021-24029
Published
Mar 15, 2021
Updated
Aug 3, 2024
Vendor
Meta Platforms, Inc.
Product
Proxygen
Classifications
CWE-617, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <v2021.03.15.00

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Meta Platforms, Inc. · Proxygenversion=unspecified <v2021.03.15.00
Meta Platforms, Inc. · mvfstversion=unspecified <a67083ff4b8dcbb7ee2839da6338032030d712b0

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-617Reachable Assertion
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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