GHSA-8JWH-2PR5-8FQ7
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-13 09:32In the Linux kernel, the following vulnerability has been resolved:
SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2
gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags byte at ptr[2], and padding at ptr[3..7], then passes ptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg(). None of these accesses check read_token->len first.
The minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus ctx->krb5e->cksum_len (12-24, depending on the enctype). All callers accept shorter tokens from the wire:
-
gss_unwrap_resp_integ() enforces only an upper bound (offset + len <= rcv_buf->len) before allocating mic.data = kmalloc(len) and passing it to gss_verify_mic(). A malicious NFS server can therefore supply a short checksum opaque, producing a small slab allocation that the Kerberos MIC verifier reads past.
-
gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400) before passing the wire-supplied length to gss_validate_seqno_mic(), which constructs a mic xdr_netobj and calls gss_verify_mic().
-
svcauth_gss_verify_header() enforces only checksum.len >= XDR_UNIT (4 bytes) before dispatching to gss_verify_mic().
-
svcauth_gss_unwrap_integ() checks only that the checksum fits in gsd->gsd_scratch.
Add a length guard at the top of gss_krb5_verify_mic_v2(), before any ptr[] access or scatterlist construction. Well-formed MIC tokens from gss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN + cksum_len bytes, so valid traffic is unaffected.
{
"affected": [],
"aliases": [
"CVE-2026-89537"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:19:36Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2\n\ngss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags\nbyte at ptr[2], and padding at ptr[3..7], then passes\nptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg().\nNone of these accesses check read_token-\u003elen first.\n\nThe minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus\nctx-\u003ekrb5e-\u003ecksum_len (12-24, depending on the enctype). All callers\naccept shorter tokens from the wire:\n\n - gss_unwrap_resp_integ() enforces only an upper bound\n (offset + len \u003c= rcv_buf-\u003elen) before allocating\n mic.data = kmalloc(len) and passing it to gss_verify_mic().\n A malicious NFS server can therefore supply a short checksum\n opaque, producing a small slab allocation that the Kerberos MIC\n verifier reads past.\n\n - gss_validate() enforces only len \u003c= RPC_MAX_AUTH_SIZE (400)\n before passing the wire-supplied length to\n gss_validate_seqno_mic(), which constructs a mic xdr_netobj\n and calls gss_verify_mic().\n\n - svcauth_gss_verify_header() enforces only\n checksum.len \u003e= XDR_UNIT (4 bytes) before dispatching to\n gss_verify_mic().\n\n - svcauth_gss_unwrap_integ() checks only that the checksum fits\n in gsd-\u003egsd_scratch.\n\nAdd a length guard at the top of gss_krb5_verify_mic_v2(), before any\nptr[] access or scatterlist construction. Well-formed MIC tokens from\ngss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN +\ncksum_len bytes, so valid traffic is unaffected.",
"id": "GHSA-8jwh-2pr5-8fq7",
"modified": "2026-09-13T09:32:17Z",
"published": "2026-09-11T21:31:31Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89537"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7a946b2e7207f968902f2147ab9b30726f82f7ab"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b94f6719dcd9f7a609bc5f459f85795900e77d25"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.