OpenSSL QUIC Server Vulnerability: Double Free in Packet Processing
CVE-2026-18798

7.5HIGH

Key Information:

Vendor

OpenSSL
Status
OpenSSL
Vendor
CVE Published:
25 August 2026

What is CVE-2026-18798?

The OpenSSL QUIC server contains a vulnerability where a double free of a QRX object occurs during the validation of an initial packet. This situation arises when the server attempts to establish a channel upon receiving a malformed packet that does not comply with RFC 9000. If the initial packet is invalid (specifically, if the destination connection ID is shorter than 8 bytes), the server's error handling routine triggers a second attempt to free the already released QRX object. This logic flaw can lead to heap corruption, causing the QUIC server process to terminate unexpectedly, resulting in a Denial of Service condition.

Affected Version(s)

OpenSSL 4.0.0 < 4.0.2

OpenSSL 3.6.0 < 3.6.4

OpenSSL 3.5.0 < 3.5.8

References

https://openssl-library.org/news/secadv/20260825.txt
vendor-advisory
https://github.com/openssl/openssl/commit/a14a1deac403522...
patch
https://github.com/openssl/openssl/commit/70cebd74d3592f5...
patch

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Fuzz0x (ZKSC Institute of Security Research)
Emilio Galle
Feng Xue (ThreatBoon)
Alexandr Nedvedicky
.