{"id":"JLSEC-2026-1086","summary":"libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow...","details":"libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the `ssh2_cipher_crypt()` function in `src/openssl.c` that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a `near-SIZE_MAX` length argument, causing immediate process crash before any authentication occurs.","modified":"2026-07-31T18:20:49.692565064Z","published":"2026-07-31T18:09:08.751Z","upstream":["CVE-2026-66033","EUVD-2026-48720","GHSA-2g8c-wcg8-r65c"],"database_specific":{"license":"CC-BY-4.0","sources":[{"imported":"2026-07-31T17:07:21.927Z","modified":"2026-07-30T15:44:47.257Z","published":"2026-07-24T17:17:35.263Z","url":"https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-66033","html_url":"https://nvd.nist.gov/vuln/detail/CVE-2026-66033","database_specific":{"status":"Analyzed"},"id":"CVE-2026-66033"},{"id":"GHSA-2g8c-wcg8-r65c","imported":"2026-07-31T17:07:29.882Z","modified":"2026-07-24T18:31:41Z","published":"2026-07-24T18:31:29Z","url":"https://api.github.com/advisories/GHSA-2g8c-wcg8-r65c","html_url":"https://github.com/advisories/GHSA-2g8c-wcg8-r65c"},{"url":"https://euvdservices.enisa.europa.eu/api/enisaid?id=EUVD-2026-48720","html_url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-48720","id":"EUVD-2026-48720","imported":"2026-07-31T17:07:23.846Z","modified":"2026-07-28T01:06:25Z","published":"2026-07-24T16:35:28Z"}]},"references":[{"type":"WEB","url":"https://github.com/advisories/GHSA-2g8c-wcg8-r65c"},{"type":"WEB","url":"https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6"},{"type":"WEB","url":"https://github.com/libssh2/libssh2/pull/2401"},{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-66033"},{"type":"WEB","url":"https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation"}],"affected":[{"package":{"name":"LibSSH2_jll","ecosystem":"Julia","purl":"pkg:julia/LibSSH2_jll?uuid=29816b5a-b9ab-546f-933c-edad1886dfa8"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.11.104+0"}]}],"database_specific":{"source":"https://github.com/JuliaLang/SecurityAdvisories.jl/tree/generated/osv/2026/JLSEC-2026-1086.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"}]}