Integer Underflow Affecting kernel-tools-devel package, versions <1:6.1.188-233.385.amzn2023


Severity

Recommended
0.0
high
0
10

Based on Amazon Linux security rating.

Threat Intelligence

EPSS
0.51% (42nd percentile)

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  • Snyk IDSNYK-AMZN2023-KERNELTOOLSDEVEL-20869411
  • published13 Oct 2026
  • disclosed11 Sept 2026

Introduced: 11 Sep 2026

CVE-2026-89551  (opens in a new tab)
CWE-191  (opens in a new tab)

How to fix?

Upgrade Amazon-Linux:2023 kernel-tools-devel to version 1:6.1.188-233.385.amzn2023 or higher.
This issue was patched in ALAS2023-2026-3197.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-tools-devel package and not the kernel-tools-devel package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2023 relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow

xdr_buf_trim() trims len bytes from the tail of an xdr_buf by walking the tail, pages, and head iovecs. Each per-section step uses min_t() so it never removes more bytes than that section holds, but the final accounting at the fix_len label subtracts the total bytes actually consumed from buf->len without any clamp:

fix_len:
        buf-&gt;len -= (len - trim);

When the caller has set buf->len to a value smaller than the sum of the iov_lens, (len - trim) can exceed buf->len and the unsigned subtraction wraps to near UINT_MAX. gss_krb5_unwrap_v2() reaches xdr_buf_trim() in exactly that state:

buf-&gt;head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;
buf-&gt;len = len - (GSS_KRB5_TOK_HDR_LEN + headskip);
xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);

buf->len is a small wire-derived value while the iov_lens are at page scale, so the per-section loops legitimately consume far more bytes than buf->len records. The wrapped buf->len then propagates as the authoritative stream bound into every downstream XDR decoder.

Fix by clamping the decrement so buf->len bottoms out at zero:

buf-&gt;len -= min_t(unsigned int, buf-&gt;len, len - trim);

On the normal path where the iov_lens sum to buf->len, (len - trim) is always <= buf->len and the result is identical to before. No callers change behavior outside the underflow case.

CVSS Base Scores

version 3.1