OpenSSL up to 3.4.7/3.5.8/3.6.4/4.0.2 Stream Reassembly algorithmic complexity

Summaryinfo

A vulnerability identified as problematic has been detected in OpenSSL up to 3.4.7/3.5.8/3.6.4/4.0.2. Impacted is an unknown function of the component Stream Reassembly. This manipulation causes algorithmic complexity. This vulnerability is tracked as CVE-2026-42772. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in OpenSSL up to 3.4.7/3.5.8/3.6.4/4.0.2. Affected by this vulnerability is some unknown functionality of the component Stream Reassembly. The manipulation with an unknown input leads to a algorithmic complexity vulnerability. The CWE definition for the vulnerability is CWE-407. An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached. As an impact it is known to affect availability. The summary by CVE is:

Issue summary: The QUIC stream reassembly algorithm performance deteriorates progressively as packets are arriving out of order. The worst case has a quadratic complexity proportional to the number of stream frames kept in the buffer for the received stream data. Impact summary: A remote QUIC peer that completes the handshake can create a connection-scoped CPU pressure and potentially a Denial of Service using compliant STREAM frames inside the advertised receive window, with low attacker bandwidth. CWE: CWE-407: Inefficient Algorithmic Complexity Description: OpenSSL manages received QUIC stream fragments using a doubly-linked list. While it optimizes for append operations (at the end of the list), it falls back to a head-to-tail linear search for any fragment that does not immediately follow the current `tail`. By manipulating the sequence of offsets, an attacker can force the server to perform O(n^2) operations, consuming excessive CPU time for the QUIC process. FIPS impact: no The FIPS module is not affected as the QUIC implementation is outside of the OpenSSL FIPS module boundary.

It is possible to read the advisory at openssl-library.org. This vulnerability is known as CVE-2026-42772 since 04/29/2026. The exploitation appears to be easy. The attack can be launched remotely. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/29/2026). The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 3.4.8, 3.5.9, 3.6.5 or 4.0.3 eliminates this vulnerability.

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Productinfo

Type

• Network Encryption Software

Name

• OpenSSL

Version

• 3.4.0
• 3.4.1
• 3.4.2
• 3.4.3
• 3.4.4
• 3.4.5
• 3.4.6
• 3.4.7
• 3.5.0
• 3.5.1
• 3.5.2
• 3.5.3
• 3.5.4
• 3.5.5
• 3.5.6
• 3.5.7
• 3.5.8
• 3.6.0
• 3.6.1
• 3.6.2
• 3.6.3
• 3.6.4
• 4.0.0
• 4.0.1
• 4.0.2

License

• open-source

Website

• Product: https://www.openssl.org/

CPE 2.3info

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CPE 2.2info

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