# CVE-2026-55199: libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler > A malicious SSH server can cause client CPU exhaustion via a crafted extension count in libssh2, leading to denial of service. - **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 17 Jun 2026 - **Updated:** 14 Jul 2026 - **Also known as:** ALPINE-CVE-2026-55199, AZL-90933, BELL-CVE-2026-55199, DEBIAN-CVE-2026-55199, ECHO-3e02-3a01-4ae3, GHSA-3cfq-4xx4-rmpg, JLSEC-2026-660, MINI-3847-fjg8-8j3g, OESA-2026-3222, ROOT-OS-DEBIAN-11-CVE-2026-55199, SUSE-SU-2026:22438-1, SUSE-SU-2026:3074-1, SUSE-SU-2026:3076-1, SUSE-SU-2026:3082-1, UBUNTU-CVE-2026-55199 ## What is CVE-2026-55199? CVE-2026-55199 is a high-severity denial of service vulnerability in libssh2, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops. Weakness: CWE-835 (Loop with Unreachable Exit Condition) ## Which versions are affected by CVE-2026-55199? It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `libssh2_org` | SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | All versions | 1.11.0-150000.4.32.1 | | `libssh2_org` | SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | All versions | 1.11.0-150000.4.32.1 | | `libssh2_org` | SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise High Performance Computing 15 SP5-ESPOS | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise High Performance Computing 15 SP5-LTSS | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Micro 5.3 | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Micro 5.4 | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Micro 5.5 | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Module for Basesystem 15 SP7 | All versions | 1.11.0-150600.20.3.1 | | `libssh2_org` | SUSE:Linux Enterprise Server 15 SP4-LTSS | All versions | 1.11.0-150000.4.32.1 | | `libssh2_org` | SUSE:Linux Enterprise Server 15 SP4-LTSS | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Server 15 SP5-LTSS | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Server 15 SP6-LTSS | All versions | 1.11.0-150600.20.3.1 | | `libssh2_org` | SUSE:Linux Enterprise Server for SAP Applications 15 SP4 | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Server for SAP Applications 15 SP5 | All versions | 1.11.0-150200.9.5.1 | | `libssh2_org` | SUSE:Linux Enterprise Server for SAP Applications 15 SP6 | All versions | 1.11.0-150600.20.3.1 | | `libssh2_org` | SUSE:Linux Micro 6.0 | All versions | 1.11.0-3.1 | Products: Libssh2 Libssh2. ## How do I fix CVE-2026-55199? Apply the vendor's patch. ## Is CVE-2026-55199 being exploited? There is no known exploitation of CVE-2026-55199 in the wild and no public exploit code. ## Other vulnerabilities in libssh2 - [CVE-2026-55200](https://insights.sbomify.com/CVE-2026-55200/): libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c (critical 9.2) - [CVE-2026-66032](https://insights.sbomify.com/CVE-2026-66032/): libssh2 Double-Free Heap Corruption via sftp_open() (high 8.7) - [CVE-2026-66033](https://insights.sbomify.com/CVE-2026-66033/): libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation (high 8.7) - [CVE-2026-58050](https://insights.sbomify.com/CVE-2026-58050/): libssh2 - Integer Overflow in publickey Subsystem Attribute Allocation (high 8.3) - [CVE-2026-58051](https://insights.sbomify.com/CVE-2026-58051/): libssh2 - Free of Uninitialized Pointer in publickey List Cleanup (high 8.3) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-55199 and fix it if it is affected. What it is: CVE-2026-55199 is a high-severity denial of service vulnerability in libssh2, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-55199 in the wild and no public exploit code. Affected product: libssh2. 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-2026-55199/ (Markdown: https://insights.sbomify.com/CVE-2026-55199/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55199 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55199 - OSV: https://osv.dev/vulnerability/CVE-2026-55199 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-55199/ Summaries are generated and may contain mistakes; the official description above is the record.