Unauthenticated and Undersized DTLS 1.2 AEAD Record Causes DoS (CVE-2026-75806)

What is affected, what to do

A flaw was found in OpenSSL. A remote, unauthenticated attacker can cause a Denial of Service (DoS) by terminating an active Datagram Transport Layer Security (DTLS) session.

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

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

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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

Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.

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 remote, unauthenticated attacker can cause a Denial of Service (DoS) by terminating an active Datagram Transport Layer Security (DTLS) session. By sending an undersized network packet that is shorter than the expected cryptographic overhead, the record processing layer fails to validate the packet length and misinterprets the packet as an internal error rather than an authentication failure. This improper handling triggers a fatal alert that unexpectedly closes the targeted connection without requiring valid encryption keys.

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

Vendors and products

• Debian Openssl
• Open Source Openssl
• OpenSSL OpenSSL

Weakness classes (CWE)

• CWE-1284Improper Validation of Specified Quantity in Input

  Base

  The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.

  Entry at MITRE CWE-1284

References & sources

• openssl-library.orgOpenSSL AdvisoryVendor advisory
• github.com4.0.3 git commitPatch
• github.com3.6.5 git commitPatch
• github.com3.5.9 git commitPatch
• github.com3.4.8 git commitPatch

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. 08.10.2026Initial analysis by NVDNVD

   Newly listed as affected:

   • OpenSSL (3.4.0 – before 3.4.8; 3.5.0 – before 3.5.9; 3.6.0 – before 3.6.5; 4.0.0 – before 4.0.3; 1.1.1 – before 1.1.1zj; 3.0.0 – before 3.0.23)

   New references:

   • https://github.com/openssl/openssl/commit/04728a289a823e68137f88da016cb9ede307217d
   • https://github.com/openssl/openssl/commit/050b275cd671a6eed1d6457642d41a5a77aab972
   • https://github.com/openssl/openssl/commit/3a4589d015a9049d47b66f186cf50a8711343a1d
   • https://github.com/openssl/openssl/commit/5af82fefbaf2b5fec2fc0e1d87f112844902f01d

   and 1 more reference

   Show 6 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) 3.4.0 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) 1.1.1 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	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/04728a289a823e68137f88da016cb9ede307217d Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/050b275cd671a6eed1d6457642d41a5a77aab972 Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/3a4589d015a9049d47b66f186cf50a8711343a1d Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/5af82fefbaf2b5fec2fc0e1d87f112844902f01d Types: Patch
   Reference type	added	—	OpenSSL Software Foundation: https://openssl-library.org/news/secadv/20260929.txt Types: Vendor Advisory

   Source identifier: nvd@nist.gov

2. 29.09.2026Record modifiedCISA ADP

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

   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:L
   SSVC assessment	added	—	{"id":"CVE-2026-75806","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-29T16:52:47.298458Z"}

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

3. 29.09.2026Receivedopenssl.org

   Weakness type: CWE-1284

   Description added or changed

   New references:

   • https://github.com/openssl/openssl/commit/04728a289a823e68137f88da016cb9ede307217d
   • https://github.com/openssl/openssl/commit/050b275cd671a6eed1d6457642d41a5a77aab972
   • https://github.com/openssl/openssl/commit/3a4589d015a9049d47b66f186cf50a8711343a1d
   • https://github.com/openssl/openssl/commit/5af82fefbaf2b5fec2fc0e1d87f112844902f01d

   and 1 more reference

   Show 8 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Description	added	—	Issue summary: An established DTLS 1.2 association using an AEAD cipher suite can be terminated by a single unauthenticated datagram whose encrypted fragment is shorter than the mandatory explicit IV and authentication tag overhead. Impact summary: An attacker who can send a datagram that is routed to an existing DTLS 1.2 association can tear that association down without knowing any key material. This is a Denial of Service limited to the targeted association. There is no memory safety or confidentiality impact. CWE: CWE-1284: Improper Validation of Specified Quantity in Input Description: In TLS 1.2 and DTLS 1.2 every record protected by an AEAD cipher suite carries an explicit IV followed by the ciphertext and an authentication tag. When decrypting such a record the record layer passed the record length to the cipher implementation before checking that the record was long enough to contain the explicit IV and the tag. For a record shorter than that overhead the cipher implementation rejected the impossible length, and the record layer treated this as an internal failure and raised a fatal internal_error alert instead of treating the record as one that failed authentication. In TLS 1.2 the same record causes a fatal internal_error alert instead of the expected bad_record_mac alert. Since any undecryptable record already terminates a TLS connection, this is a protocol conformance issue rather than a security issue in TLS. The fix validates the record length against the explicit IV and tag length before any AEAD processing, so that TLS reports bad_record_mac and DTLS silently discards the record. FIPS impact: no The affected code is outside the FIPS module boundary.
   Weakness type (CWE)	added	—	CWE-1284
   Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/75xxx/CVE-2026-75806.json">CVE-2026-75806</a>
   Reference	added	—	https://github.com/openssl/openssl/commit/04728a289a823e68137f88da016cb9ede307217d
   Reference	added	—	https://github.com/openssl/openssl/commit/050b275cd671a6eed1d6457642d41a5a77aab972
   Reference	added	—	https://github.com/openssl/openssl/commit/3a4589d015a9049d47b66f186cf50a8711343a1d
   Reference	added	—	https://github.com/openssl/openssl/commit/5af82fefbaf2b5fec2fc0e1d87f112844902f01d
   Reference	added	—	https://openssl-library.org/news/secadv/20260929.txt

   Source identifier: openssl-security@openssl.org