bzip2: Double Free (CVE-2026-18798)

What is affected, what to do

A flaw was found in OpenSSL. A malformed INITIAL packet with an invalid DCID (destination connection ID) can cause the QUIC server to double free the QRX object.

Update OpenSSL to version 4.0.2, OpenSSL to version 3.6.4, OpenSSL to version 3.5.8.

Affected

• OpenSSL lt 4.0.0..4.0.2
• OpenSSL lt 3.6.0..3.6.4
• OpenSSL lt 3.5.0..3.5.8

Fixed in

• OpenSSL 4.0.2
• OpenSSL 3.6.4
• OpenSSL 3.5.8

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A flaw was found in OpenSSL. A malformed INITIAL packet with an invalid DCID (destination connection ID) can cause the QUIC server to double free the QRX object. This issue leads to memory corruption, causing the termination of the QUIC server process and resulting in a denial of service.

Source: BSI WID Portal

Vendors and products

• Debian Openssl
• Freebsd Project Freebsd OS
• Meinberg Lantime
• Open Source Openssl
• OpenSSL OpenSSL
• Ubuntu Openssl

Weakness classes (CWE)

• CWE-415Double Free

  Variant

  The product calls free() twice on the same memory address.

  Entry at MITRE CWE-415

References & sources

• openssl-library.orgOpenSSL AdvisoryVendor advisory
• github.com4.0.2 git commitPatch
• github.com3.6.4 git commitPatch
• github.com3.5.8 git commitPatch
• github.com3.4.7 git commitPatch
• github.com3.0.22 git commitPatch
• openssh.orgreleasenotes.htmlProduct, Release notes
• github.com4.0.2 git commitPatch
• github.com3.6.4 git commitPatch
• github.com3.5.8 git commitPatch
• github.com3.4.7 git commitPatch
• github.com3.0.22 git commitPatch
• github.comGNOME/libxml2/compare/v2.15.3...v2.15.4
• github.comGNOME/libxml2/commit/b63cd517afecb76582dd9488c55e54ceaf50de61
• curl.sejson
• curl.sewww
• hackerone.comissue
• github.comutil-linux/util-linux/security/advisories/GHSA-8gj5-72r3-428gx_refsource_CONFIRM
• github.comutil-linux/util-linux/commit/0b010025a0e429bc80355c94db86a84339…x_refsource_MISC
• github.comutil-linux/util-linux/commit/0d3d55975aa3492c62fd345eac38f41cd1…x_refsource_MISC

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

1. 23.09.2026Initial analysis by NVDNVD

   Newly listed as affected:

   • OpenSSL (3.5.0 – before 3.5.8; 3.6.0 – before 3.6.4; 4.0.0 – before 4.0.2)

   New references:

   • https://github.com/openssl/openssl/commit/70cebd74d3592f5272945501b58a60374c4e13af
   • https://github.com/openssl/openssl/commit/967582d5037f01a26b6d19beae19af62a1b15c3c
   • https://github.com/openssl/openssl/commit/a14a1deac403522fbeafabcb198503cf6caa7dc4
   • https://openssl-library.org/news/secadv/20260825.txt
   Show 5 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Product configuration	added	—	OR *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.5.0 up to (excluding) 3.5.8 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.6.0 up to (excluding) 3.6.4 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 4.0.0 up to (excluding) 4.0.2
   Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/70cebd74d3592f5272945501b58a60374c4e13af Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/967582d5037f01a26b6d19beae19af62a1b15c3c Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/a14a1deac403522fbeafabcb198503cf6caa7dc4 Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://openssl-library.org/news/secadv/20260825.txt Types: Vendor Advisory

   Source identifier: nvd@nist.gov

2. 25.08.2026Record modifiedCISA ADP

   CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

   CISA assessment (SSVC): exploitation: none known, automatable: yes

   Show 2 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   CVSS	added	—	AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
   SSVC assessment	added	—	{"id":"CVE-2026-18798","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-08-25T14:15:00.501697Z"}

   Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

3. 25.08.2026Receivedopenssl.org

   Weakness type: CWE-415

   Description added or changed

   New references:

   • https://github.com/openssl/openssl/commit/70cebd74d3592f5272945501b58a60374c4e13af
   • https://github.com/openssl/openssl/commit/967582d5037f01a26b6d19beae19af62a1b15c3c
   • https://github.com/openssl/openssl/commit/a14a1deac403522fbeafabcb198503cf6caa7dc4
   • https://openssl-library.org/news/secadv/20260825.txt
   Show 7 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Affected versions (publisher)	added	—	OpenSSL
   Description	added	—	Issue summary: QUIC server may double free QRX (QUIC record layer RX) object when channel creation fails for initial packet. Impact summary: Double free leads to heap corruption, which typically results in termination of QUIC server process, leading to Denial of Service. There is so far no evidence that this double free is exploitable for remote code execution, thus it is considered highly improbable. CWE: CWE-415: Double Free Description: In order to validate initial packet, OpenSSL QUIC stack default packet handler (port_default_packet_handler()) creates a so-called QRX object. If the initial packet validates successfully with QRX object, the default packet handler proceeds to channel (connection object) creation. The QRX object used for packet validation is passed to port_bind_channel(), so it becomes part of the newly created connection. If port_bind_channel() fails, then it also frees the QRX object. Once port_bind_channel() returns, the port_default_packet_handler() detects the failure and proceeds to the error branch, where the same QRX object is freed for the second time. The failure in port_bind_channel() function can be induced with a relatively low effort by a malformed (non RFC 9000 compliant) INITIAL packet. If the packet carries DCID (destination connection ID) which is shorter than 8 bytes, then port_bind_channel() jumps to the error path after ossl_quic_lcidm_enrol_odcid() detects that the DCID has invalid length. FIPS impact: no The FIPS module is not affected, as the QUIC implementation is outside of the OpenSSL FIPS module boundary.
   Weakness type (CWE)	added	—	CWE-415
   Reference	added	—	https://github.com/openssl/openssl/commit/70cebd74d3592f5272945501b58a60374c4e13af
   Reference	added	—	https://github.com/openssl/openssl/commit/967582d5037f01a26b6d19beae19af62a1b15c3c
   Reference	added	—	https://github.com/openssl/openssl/commit/a14a1deac403522fbeafabcb198503cf6caa7dc4
   Reference	added	—	https://openssl-library.org/news/secadv/20260825.txt

   Source identifier: openssl-security@openssl.org