# CVE-2026-2673: OpenSSL TLS 1.3 server may choose unexpected key agreement group - **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L`) - **Exploited in the wild:** Not known - **Fix available:** Yes - **Published:** 13 Mar 2026 - **Updated:** 18 May 2026 - **Also known as:** ALPINE-CVE-2026-2673, BELL-CVE-2026-2673, DEBIAN-CVE-2026-2673, GHSA-wj64-gh9j-xm82, JLSEC-2026-271, MINI-m8jj-632g-59cq, UBUNTU-CVE-2026-2673 ## What is CVE-2026-2673? CVE-2026-2673 is a medium-severity vulnerability in Openssl Openssl, published on 13 Mar 2026. ### Official description Issue summary: An OpenSSL TLS 1.3 server may fail to negotiate the expected preferred key exchange group when its key exchange group configuration includes the default by using the 'DEFAULT' keyword. Impact summary: A less preferred key exchange may be used even when a more preferred group is supported by both client and server, if the group was not included among the client's initial predicated keyshares. This will sometimes be the case with the new hybrid post-quantum groups, if the client chooses to defer their use until specifically requested by the server. If an OpenSSL TLS 1.3 server's configuration uses the 'DEFAULT' keyword to interpolate the built-in default group list into its own configuration, perhaps adding or removing specific elements, then an implementation defect causes the 'DEFAULT' list to lose its 'tuple' structure, and all server-supported groups were treated as a single sufficiently secure 'tuple', with the server not sending a Hello Retry Request (HRR) even when a group in a more preferred tuple was mutually supported. As a result, the client and server might fail to negotiate a mutually supported post-quantum key agreement group, such as 'X25519MLKEM768', if the client's configuration results in only 'classical' groups (such as 'X25519' being the only ones in the client's initial keyshare prediction). OpenSSL 3.5 and later support a new syntax for selecting the most preferred TLS 1.3 key agreement group on TLS servers. The old syntax had a single 'flat' list of groups, and treated all the supported groups as sufficiently secure. If any of the keyshares predicted by the client were supported by the server the most preferred among these was selected, even if other groups supported by the client, but not included in the list of predicted keyshares would have been more preferred, if included. The new syntax partitions the groups into distinct 'tuples' of roughly equivalent security. Within each tuple the most preferred group included among the client's predicted keyshares is chosen, but if the client supports a group from a more preferred tuple, but did not predict any corresponding keyshares, the server will ask the client to retry the ClientHello (by issuing a Hello Retry Request or HRR) with the most preferred mutually supported group. The above works as expected when the server's configuration uses the built-in default group list, or explicitly defines its own list by directly defining the various desired groups and group 'tuples'. No OpenSSL FIPS modules are affected by this issue, the code in question lies outside the FIPS boundary. OpenSSL 3.6 and 3.5 are vulnerable to this issue. OpenSSL 3.6 users should upgrade to OpenSSL 3.6.2 once it is released. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.6 once it is released. OpenSSL 3.4, 3.3, 3.0, 1.0.2 and 1.1.1 are not affected by this issue. Weakness: CWE-757 (Selection of Less-Secure Algorithm During Negotiation) ## Which versions are affected by CVE-2026-2673? It affects 2 products. Products: Openssl Openssl, Siemens Simatic Cn 4100 Firmware. ## How do I fix CVE-2026-2673? Upgrade to a fixed version. ## Is CVE-2026-2673 being exploited? There is no known exploitation of CVE-2026-2673 in the wild and no public exploit code. ## Other vulnerabilities in Openssl Openssl - [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0) - [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0) - [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8) - [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8) - [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-2673 and fix it if it is affected. What it is: CVE-2026-2673 is a medium-severity vulnerability in Openssl Openssl, published on 13 Mar 2026. Exploitation: There is no known exploitation of CVE-2026-2673 in the wild and no public exploit code. Affected product: Openssl Openssl. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-2673/ (Markdown: https://insights.sbomify.com/CVE-2026-2673/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2673 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2673 - OSV: https://osv.dev/vulnerability/CVE-2026-2673 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-2673/ Summaries are generated and may contain mistakes; the official description above is the record.