{"id":"AZL-100338","summary":"CVE-2026-89551 affecting package kernel 6.6.150.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: xdr_buf_trim: clamp buf-\u003elen to avoid underflow\n\nxdr_buf_trim() trims `len` bytes from the tail of an xdr_buf by\nwalking the tail, pages, and head iovecs.  Each per-section step\nuses min_t() so it never removes more bytes than that section\nholds, but the final accounting at the fix_len label subtracts the\ntotal bytes actually consumed from buf-\u003elen without any clamp:\n\n    fix_len:\n            buf-\u003elen -= (len - trim);\n\nWhen the caller has set buf-\u003elen to a value smaller than the sum\nof the iov_lens, (len - trim) can exceed buf-\u003elen and the unsigned\nsubtraction wraps to near UINT_MAX.  gss_krb5_unwrap_v2() reaches\nxdr_buf_trim() in exactly that state:\n\n    buf-\u003ehead[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;\n    buf-\u003elen = len - (GSS_KRB5_TOK_HDR_LEN + headskip);\n    xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);\n\nbuf-\u003elen is a small wire-derived value while the iov_lens are at\npage scale, so the per-section loops legitimately consume far more\nbytes than buf-\u003elen records.  The wrapped buf-\u003elen then propagates\nas the authoritative stream bound into every downstream XDR\ndecoder.\n\nFix by clamping the decrement so buf-\u003elen bottoms out at zero:\n\n    buf-\u003elen -= min_t(unsigned int, buf-\u003elen, len - trim);\n\nOn the normal path where the iov_lens sum to buf-\u003elen, (len - trim)\nis always \u003c= buf-\u003elen and the result is identical to before.  No\ncallers change behavior outside the underflow case.","modified":"2026-09-13T06:06:36Z","published":"2026-09-11T20:19:38Z","upstream":["CVE-2026-89551"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89551"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.150.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-100338.json"}}],"schema_version":"1.9.0"}