{"id":"CVE-2026-89538","title":"SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Reject krb5 v2 wrap tokens with oversized ec field\n\ngss_krb5_unwrap_v2() sets buf->len to a logical\nlength, which can be much smaller than head[0].iov_len\n(the …","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-131"],"vendor":"Linux","product":"Linux","affected":["Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < ac9efc29346b6942e71f0e24a3178a9121330fab","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < b5746095b59f4d11f39f08751d36bbdfd1e5deac","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 4abb44a29bb515df6f49123848765c70fc9b5021","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < dfcd81ab45613d45996fbf483d4ef54b0ec90ab9","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 1f9856af065b6158271687e9788407b9573fd16f","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 880effc943ed82d6811f272ed3307c222b40f4d6","Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < ad484748eec0a66eac0f13ab53b3fbedb7333c91","Linux 3.13"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"total","timestamp":"2026-10-16T19:23:19.852732Z"},"published":"2026-09-11","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:48:29.976Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89538","references":[{"url":"https://git.kernel.org/stable/c/ac9efc29346b6942e71f0e24a3178a9121330fab"},{"url":"https://git.kernel.org/stable/c/b5746095b59f4d11f39f08751d36bbdfd1e5deac"},{"url":"https://git.kernel.org/stable/c/9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296"},{"url":"https://git.kernel.org/stable/c/4abb44a29bb515df6f49123848765c70fc9b5021"},{"url":"https://git.kernel.org/stable/c/dfcd81ab45613d45996fbf483d4ef54b0ec90ab9"},{"url":"https://git.kernel.org/stable/c/1f9856af065b6158271687e9788407b9573fd16f"},{"url":"https://git.kernel.org/stable/c/880effc943ed82d6811f272ed3307c222b40f4d6"},{"url":"https://git.kernel.org/stable/c/ad484748eec0a66eac0f13ab53b3fbedb7333c91"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89538.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89538"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532114"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89538"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89538"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89538.mbox"}],"tags":["cve.org","csaf","vex","red-hat","score-dispute"],"epss":0.00714,"epssPercentile":0.53473,"scores":{"cna":9.8,"vendor":7},"ingestedAt":"2026-09-14T15:23:07.452Z","slug":"CVE-2026-89538","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Reject krb5 v2 wrap tokens with oversized ec field\n\ngss_krb5_unwrap_v2() sets buf->len to a logical\nlength, which can be much smaller than head[0].iov_len\n(the allocated receive-page capacity).  It then calls\nxdr_buf_trim() with a trim length derived from the 16-bit\n\"extra count\" (ec) field in the Kerberos v2 token header.\n\nThe ec field is authenticated by the post-decrypt memcmp()\nagainst the encrypted header copy, so a randomly-mutated\nvalue is rejected.  However, any peer holding a valid GSS\ncontext can legitimately encrypt a token whose ec exceeds\nthe plaintext length.  Per RFC 4121, such a token is\nstructurally malformed.\n\nAlthough xdr_buf_trim() now clamps the buf->len subtraction\nto avoid unsigned underflow, the buffer is still left in a\nsemantically invalid state (zero length, inconsistent iov\nlengths) when ec is oversized.\n\nReject these tokens before calling xdr_buf_trim(), giving\ncallers a well-defined GSS_S_DEFECTIVE_TOKEN error and\nkeeping the xdr_buf internally consistent.  The wrapped blob\nbegins at a nonzero offset -- both callers pass len as\noffset + opaque_len -- so buf->len still counts the offset\nbytes that precede the blob.  Compare the trim length\nagainst the remaining wrapped segment, buf->len - offset,\nrather than the whole buffer; comparing against buf->len\nalone leaves an offset-wide window in which an oversized ec\npasses the test and xdr_buf_trim() cuts into the bytes ahead\nof the blob.\n\n## Affected\n\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < ac9efc29346b6942e71f0e24a3178a9121330fab`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < b5746095b59f4d11f39f08751d36bbdfd1e5deac`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 4abb44a29bb515df6f49123848765c70fc9b5021`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < dfcd81ab45613d45996fbf483d4ef54b0ec90ab9`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 1f9856af065b6158271687e9788407b9573fd16f`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < 880effc943ed82d6811f272ed3307c222b40f4d6`\n- `Linux >= cf4c024b908353fcc48309374d39e3399d67dfd1 < ad484748eec0a66eac0f13ab53b3fbedb7333c91`\n- `Linux 3.13`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, … · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89538.json)","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":223300,"id":"CVE-2026-89538","ts":1792180049938,"field":"cvss","old":"7","new":"9.8"},{"seq":223299,"id":"CVE-2026-89538","ts":1792180049938,"field":"severity","old":"high","new":"critical"},{"seq":208110,"id":"CVE-2026-89538","ts":1789922711599,"field":"cvss","old":"9.8","new":"7"},{"seq":208109,"id":"CVE-2026-89538","ts":1789922711599,"field":"severity","old":"critical","new":"high"},{"seq":197963,"id":"CVE-2026-89538","ts":1789384321170,"field":"cvss","old":"5.3","new":"9.8"},{"seq":197962,"id":"CVE-2026-89538","ts":1789384321170,"field":"severity","old":"medium","new":"critical"},{"seq":183758,"id":"CVE-2026-89538","ts":1789356677264,"field":"cvss","old":"9.8","new":"5.3"},{"seq":183757,"id":"CVE-2026-89538","ts":1789356677264,"field":"severity","old":"critical","new":"medium"},{"seq":153336,"id":"CVE-2026-89538","ts":1789285350097,"field":"cvss","old":null,"new":"9.8"},{"seq":153335,"id":"CVE-2026-89538","ts":1789285350097,"field":"severity","old":"none","new":"critical"},{"seq":147772,"id":"CVE-2026-89538","ts":1789270212230,"field":"cvss","old":null,"new":"5.3"},{"seq":147771,"id":"CVE-2026-89538","ts":1789270212230,"field":"severity","old":"none","new":"medium"},{"seq":109526,"id":"CVE-2026-89538","ts":1789183732286,"field":"cvss","old":null,"new":"5.3"},{"seq":109525,"id":"CVE-2026-89538","ts":1789183732286,"field":"severity","old":"none","new":"medium"}]}