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CVE-2026-89538— SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于gss_krb5_unwrap_v2()对Kerberos v2令牌头中过大的ec字段处理不当，未在调用xdr_buf_trim()前拒绝该令牌，可能导致缓冲区处于零长度、iov长度不一致的无效状态。

CVSS 9.8 · Critical EPSS 0.70% · P52

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux cf4c024b908353fcc48309374d39e3399d67dfd1< ac9efc29346b6942e71f0e24a3178a9121330fab affected
cf4c024b908353fcc48309374d39e3399d67dfd1< b5746095b59f4d11f39f08751d36bbdfd1e5deac affected
cf4c024b908353fcc48309374d39e3399d67dfd1< 9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296 affected
cf4c024b908353fcc48309374d39e3399d67dfd1< 4abb44a29bb515df6f49123848765c70fc9b5021 affected
cf4c024b908353fcc48309374d39e3399d67dfd1< dfcd81ab45613d45996fbf483d4ef54b0ec90ab9 affected
cf4c024b908353fcc48309374d39e3399d67dfd1< 1f9856af065b6158271687e9788407b9573fd16f affected
cf4c024b908353fcc48309374d39e3399d67dfd1< 880effc943ed82d6811f272ed3307c222b40f4d6 affected
cf4c024b908353fcc48309374d39e3399d67dfd1< ad484748eec0a66eac0f13ab53b3fbedb7333c91 affected
… +10 more rows
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I. Basic Information for CVE-2026-89538

Vulnerability Information
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Vulnerability Title
SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field gss_krb5_unwrap_v2() sets buf->len to a logical length, which can be much smaller than head[0].iov_len (the allocated receive-page capacity). It then calls xdr_buf_trim() with a trim length derived from the 16-bit "extra count" (ec) field in the Kerberos v2 token header. The ec field is authenticated by the post-decrypt memcmp() against the encrypted header copy, so a randomly-mutated value is rejected. However, any peer holding a valid GSS context can legitimately encrypt a token whose ec exceeds the plaintext length. Per RFC 4121, such a token is structurally malformed. Although xdr_buf_trim() now clamps the buf->len subtraction to avoid unsigned underflow, the buffer is still left in a semantically invalid state (zero length, inconsistent iov lengths) when ec is oversized. Reject these tokens before calling xdr_buf_trim(), giving callers a well-defined GSS_S_DEFECTIVE_TOKEN error and keeping the xdr_buf internally consistent. The wrapped blob begins at a nonzero offset -- both callers pass len as offset + opaque_len -- so buf->len still counts the offset bytes that precede the blob. Compare the trim length against the remaining wrapped segment, buf->len - offset, rather than the whole buffer; comparing against buf->len alone leaves an offset-wide window in which an oversized ec passes the test and xdr_buf_trim() cuts into the bytes ahead of the blob.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于gss_krb5_unwrap_v2()对Kerberos v2令牌头中过大的ec字段处理不当，未在调用xdr_buf_trim()前拒绝该令牌，可能导致缓冲区处于零长度、iov长度不一致的无效状态。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux cf4c024b908353fcc48309374d39e3399d67dfd1 ~ ac9efc29346b6942e71f0e24a3178a9121330fab -
Linux Linux 3.13 -

II. Public POCs for CVE-2026-89538

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III. Intelligence Information for CVE-2026-89538

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Patches & Fixes for CVE-2026-89538 (8)

Same Patch Batch · Linux · 2026-09-11 · 431 CVEs total

CVE-2026-89688 9.8 CRITICAL nfsd: drop the stateid, not the stateowner, on seqid_op replay retry
CVE-2026-89655 9.8 CRITICAL ceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock
CVE-2026-89658 9.8 CRITICAL NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup
CVE-2026-89660 9.8 CRITICAL NFSD: Prevent client use-after-free during admin state revocation
CVE-2026-89659 9.8 CRITICAL NFSD: Prevent client use-after-free during delegation revoke
CVE-2026-89662 9.8 CRITICAL NFSD: Prevent lock owner use-after-free during client teardown
CVE-2026-89669 9.8 CRITICAL nfsd: initialize copy-notify stateid before publishing it
CVE-2026-89674 9.8 CRITICAL nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget
CVE-2026-89675 9.8 CRITICAL nfsd: fix UAF in async copy cancel and shutdown
CVE-2026-89676 9.8 CRITICAL nfsd: fix stale s2s_cp_stateids IDR entry for async COPY
CVE-2026-89677 9.8 CRITICAL nfsd: fix possible fh_compose of wrong dentry in nfsd4_create_file()
CVE-2026-89681 9.8 CRITICAL nfsd: fix layout fence worker double-reference race
CVE-2026-89686 9.8 CRITICAL nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke
CVE-2026-89703 9.8 CRITICAL nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations
CVE-2026-89479 9.8 CRITICAL sctp: stop processing a packet once its association is deleted
CVE-2026-89478 9.8 CRITICAL sctp: drop a chunk if its transport was removed
CVE-2026-89702 9.8 CRITICAL nfsd: size fh_verify server sockaddr slot by xpt_locallen
CVE-2026-89482 9.8 CRITICAL nvme-tcp: do not accept C2HData based on blk_rq_payload_bytes() alone
CVE-2026-89708 9.8 CRITICAL nfsd: RCU-protect cl_cb_session to fix use-after-free on session teardown
CVE-2026-89712 9.8 CRITICAL NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock

Showing top 20 of 431 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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