HighCVE-2026-84782

    DTLS Retransmits Handshake Messages From a Stale Buffer Offset (CVE-2026-84782)

    Published Last modified Sources: Red Hat, Debian, Msrc Update Guide, SUSE, CVE.org, Ubuntu, BSI

    What is affected, what to do

    A flaw was found in OpenSSL. The Datagram Transport Layer Security (DTLS) retransmission mechanism fails to properly handle handshake message writes that are suspended before completion.

    Update OpenSSL to version 4.0.3, OpenSSL to version 3.6.5, OpenSSL to version 3.5.9.

    Affected
    • OpenSSL lt 4.0.0..4.0.3
    • OpenSSL lt 3.6.0..3.6.5
    • OpenSSL lt 3.5.0..3.5.9
    • OpenSSL lt 3.4.0..3.4.8
    • OpenSSL lt 3.0.0..3.0.23
    • OpenSSL lt 1.1.1..1.1.1zj
    • OpenSSL lt 1.0.2..1.0.2zs
    Fixed in
    • OpenSSL 4.0.3
    • OpenSSL 3.6.5
    • OpenSSL 3.5.9
    • OpenSSL 3.4.8
    • OpenSSL 3.0.23
    • OpenSSL 1.1.1zj
    • OpenSSL 1.0.2zs

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

    Metrics

    8.2

    Priority

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

    Source: Vendor (CNA), CVSS v3

    8.2

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, Debian, Msrc Update Guide, SUSE, CVE.org, Ubuntu, BSI

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 31.7

    Show all metrics
    Severity
    High
    Priority score

    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
    79.03
    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
    8.2
    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
    8.2
    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
    0.4 %
    Low — model estimates < 1% 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
    31.7
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    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
    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-125

    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. The Datagram Transport Layer Security (DTLS) retransmission mechanism fails to properly handle handshake message writes that are suspended before completion. A remote attacker could exploit this vulnerability during handshake message retransmission, causing OpenSSL to read past the message buffer or overwrite internal state required to resume writing. This issue can result in information disclosure through out-of-bounds memory reads or cause a Denial of Service (DoS) by crashing the process.

    Source: redhat_csaf, Debian Security Advisories, Microsoft Security Update Guide, suse_csaf, NVD (NIST), cvelistv5, Ubuntu Security Notices, BSI WID Portal, BSI CSAF

    Affected products

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

    Affected products
    VendorProductAffected versionsFixed in
    OpenSSLOpenSSL
    • 1.0.2 – < 1.0.2zs
    • 1.1.1 – < 1.1.1zj
    • 3.0.0 – < 3.0.23
    • 3.4.0 – < 3.4.8
    • 3.5.0 – < 3.5.9
    • 3.6.0 – < 3.6.5
    • 4.0.0 – < 4.0.3
    • 1.0.2zs
    • 1.1.1zj
    • 3.0.23
    • 3.4.8
    • 3.5.9
    • 3.6.5
    • 4.0.3
    opensslopenssl
    • 1.0.2 – < 1.0.2zs
    • 1.1.1 – < 1.1.1zj
    • 3.0.0 – < 3.0.23
    • 3.4.0 – < 3.4.8
    • 3.5.0 – < 3.5.9
    • 3.6.0 – < 3.6.5
    • 4.0.0 – < 4.0.3
    • 1.0.2zs
    • 1.1.1zj
    • 3.0.23
    • 3.4.8
    • 3.5.9
    • 3.6.5
    • 4.0.3
    FreeBSD ProjectFreeBSD OS
    • < 15.1
    • 15.1
    Open SourceOpenSSL
    • < 1.0.2zs
    • < 1.1.1zj
    • < 3.0.23
    • < 3.4.8
    • < 3.5.9
    • < 3.6.5
    • < 4.0.3
    • 1.0.2zs
    • 1.1.1zj
    • 3.0.23
    • 3.4.8
    • 3.5.9
    • 3.6.5
    • 4.0.3

    Weakness classes (CWE)

    • CWE-125Out-of-bounds Read

      Base

      The product reads data past the end, or before the beginning, of the intended buffer.

      Entry at MITRE CWE-125

    References & sources

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. Initial Analysisnvd@nist.gov

      • CPE Configuration: after OR *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.4.0 up to (excluding) 3.4.8 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.5.0 up to (excluding) 3.5.9 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.6.0 up to (excluding) 3.6.5 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 4.0.0 up to (excluding) 4.0.3 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 1.0.2 up to (excluding) 1.0.2zs *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 1.1.1 up to (excluding) 1.1.1zj *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.0.0 up to (excluding) 3.0.23
      • Reference Type: after OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/906cf0ef1c85ca40ce69163e9086d6d3fe292943 Types: Patch
      • Reference Type: after OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/9f6b34422af7eb5dac61322e33dac1ae989fa628 Types: Patch
      • Reference Type: after OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/a383dafdd754eb5b22bf45e37e1bff9d07277a58 Types: Patch

    2. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • CVSS V3.1: after AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
      • SSVC: after {"id":"CVE-2026-84782","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technical…

    3. New CVE Receivedopenssl-security@openssl.org

      • Description: after Issue summary: The DTLS retransmission logic does not correctly handle a handshake message write that is suspended part-way through. The retransmitted message can be read past the message buffer and the retransmission overwrites the internal state the suspended write needs to resume correctly. Impact summary: The retransmitted message can disclose a heap memory to the peer as plaintext handshake data or cause a crash and a Denial of Service when the read reaches an unmapped memory region. CWE: CWE-125: Out-of-bounds Read Description: DTLS handshake messages can be written out in multiple fragments, and a write can suspend mid-message (returning WANT_WRITE) if the underlying transport temporarily cannot accept more data. While such a write is suspended, the DTLS retransmission timer may independently fire and ask the retransmission logic to resend an earlier, already-acknowledged-as-sent message from its retransmit queue. The retransmission logic reused the same internal buffer and position tracking as the message that was still being written, without resetting the position back to the start of the message being retransmitted. As a result the retransmission was read starting from wherever the suspended write had left off, producing a mislabelled message whose body was leftover bytes from the other, larger message still in flight - content that was never meant to be sent at that point, and which could run past the end of the allocated buffer. Separately, even when the retransmission is positioned correctly, allowing it to run to completion while another write is suspended overwrites the same shared bookkeeping that the suspended write depends on to resume. When the application later resumes the suspended write (via a subsequent SSL_read(), SSL_write(), SSL_accept(), or SSL_connect() call), it finds that bookkeeping in a state inconsistent with the message and aborts the process in a debugging build. The fix resets the retransmission's read position to the start of the message before resending, and skips retransmission entirely whenever a handshake write is still suspended, deferring to the next call that resumes it instead. FIPS impact: no The affected code is outside the FIPS module boundary.
      • CWE: after CWE-125
      • Affected: after New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/84xxx/CVE-2026-84782.json">CVE-2026-84782</a>
      • Reference: after https://github.com/openssl/openssl/commit/906cf0ef1c85ca40ce69163e9086d6d3fe292943