HighCVE-2026-18798

    FreeBSD: Double Free (CVE-2026-18798)

    Published Last modified Sources: BSI

    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

    7.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: BSI

    1.7 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 77.1

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    80.39 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    1.7 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    77.1
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 25 August 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-415

    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

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    FreeBSDFreeBSD
    • ≥ 14.4-RELEASE
    • ≥ 15.0-RELEASE
    • ≥ 15.1-RELEASE
    • —
    • —
    • —
    OpenSSLOpenSSL
    • 1.0.2 – < 1.0.2zr
    • 1.1.1 – < 1.1.1zi
    • 3.0.0 – < 3.0.22
    • 3.4.0 – < 3.4.7
    • 3.5.0 – < 3.5.8
    • 3.6.0 – < 3.6.4
    • 4.0.0 – < 4.0.2
    • 1.0.2zr
    • 1.1.1zi
    • 3.0.22
    • 3.4.7
    • 3.5.8
    • 3.6.4
    • 4.0.2
    opensslopenssl
    • 1.0.2 – < 1.0.2zr
    • 1.1.1 – < 1.1.1zi
    • 3.0.0 – < 3.0.22
    • 3.4.0 – < 3.4.7
    • 3.5.0 – < 3.5.8
    • 3.6.0 – < 3.6.4
    • 4.0.0 – < 4.0.2
    • 1.0.2zr
    • 1.1.1zi
    • 3.0.22
    • 3.4.7
    • 3.5.8
    • 3.6.4
    • 4.0.2
    FreeBSD ProjectFreeBSD OS
    • < 14.4-RELEASE-p9
    • < 14.4-STABLE
    • < 15.0-RELEASE-p13
    • < 15.1-RELEASE-p3
    • < 15.1-STABLE
    • 14.4-RELEASE-p9
    • 14.4-STABLE
    • 15.0-RELEASE-p13
    • 15.1-RELEASE-p3
    • 15.1-STABLE
    MeinbergLANTIME
    • < V7.10.016
    • V7.10.016
    Open SourceOpenSSL
    • < 1.0.2zr
    • < 1.1.1zi
    • < 3.0.22
    • < 3.4.7
    • < 3.5.8
    • < 3.6.4
    • < 4.0.2
    • 1.0.2zr
    • 1.1.1zi
    • 3.0.22
    • 3.4.7
    • 3.5.8
    • 3.6.4
    • 4.0.2
    OracleCommunications
    • 11
    • 14
    • 15.0.0.0.0
    • 15.0.1.0.0
    • 15.1.0.0.0
    • 15.2.0.0.0
    • 24.2.4-25.2.000
    • 25.1.100
    • 25.1.200
    • 25.2.100
    • 25.2.200
    • 25.2.201
    • 25.2.202
    • 26.1.200
    • 26.1.202
    • 47.0.0.2.0
    • 6
    • 6.1
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    BSDfreebsdfreebsd14.4
    BSDfreebsdfreebsd15.1
    BSDfreebsdfreebsd15.0
    Linuxdebianopensslbookworm
    Linuxdebianopenssltrixie
    Linuxubuntuopenssljammy
    Linuxubuntuopensslnoble
    Linuxubuntuopensslresolute

    Weakness classes (CWE)

    References & sources

    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. Initial 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)
      Show 5 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationadded
      —
      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 typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/70cebd74d3592f5272945501b58a60374c4e13af Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/967582d5037f01a26b6d19beae19af62a1b15c3c Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/a14a1deac403522fbeafabcb198503cf6caa7dc4 Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://openssl-library.org/news/secadv/20260825.txt Types: Vendor Advisory

      Source identifier: nvd@nist.gov

    2. Record 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
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
      SSVC assessmentadded
      —
      {"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. Receivedopenssl.org

      Weakness type: CWE-415

      Description added or changed

      Show 7 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      OpenSSL
      Descriptionadded
      —
      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
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/70cebd74d3592f5272945501b58a60374c4e13af
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/967582d5037f01a26b6d19beae19af62a1b15c3c
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/a14a1deac403522fbeafabcb198503cf6caa7dc4
      Referenceadded
      —
      https://openssl-library.org/news/secadv/20260825.txt

      Source identifier: openssl-security@openssl.org

    Linked CVEs

    Linked CVEs
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    HighCVE-2026-63075QUIC ACK-only Packet Retention Can Cause Memory Exhaustion7.5—
    MediumCVE-2026-63074CMP Indefinite Cache Growth of ExtraCerts5.9—
    HighCVE-2026-63073Untrusted Sender DN Used as Format String in CMP Response Validation7.4—
    HighCVE-2026-63072Heap Buffer Overflow in CMS Key Unwrapping7.5—
    HighCVE-2026-58097ppp(8): missing length validation in mp_SetEnddisc()7.8—
    HighCVE-2026-58096ppp(8): missing length validation in LcpDecodeConfig()8.8—
    HighCVE-2026-58095ppp(8): incorrect length calculation in mp_Enddisc()8.8—
    HighCVE-2026-58094TOCTOU race in POSIX shared memory large page configuration7.8—
    HighCVE-2026-58093Kernel use-after-free via tty ioctls7.0—
    HighCVE-2026-58092Unauthorized credential switching8.1—
    HighCVE-2026-58091Kernel use-after-free via the SNDCTL_DSP_SYNCSTART ioctl7.8—
    HighCVE-2026-58090Use-after-free in unix SOCK_STREAM message handling7.8—
    HighCVE-2026-58089hwpmc fails to detach PMCs during exec credential transitions7.8—
    HighCVE-2026-54874Excessive Memory Use Buffering DTLS Records for a Future Epoch7.5—
    HighCVE-2026-18798QUIC Server May Trigger Double Free When Processing INITIAL Packet7.5—
    HighCVE-2026-14457RPK Server Signature Algorithm Selection Can Dereference a Missing Certificate7.5—
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