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Vulnerabilities

Vulnerability · CVE-2026-63887

scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf

Published Jul 19, 2026 · catalog updated Oct 22, 2026 · linux kernel

Check if you run it

No confirmed exploitation is on record for CVE-2026-63887. EPSS is 0.78%. Act only if a listed version of linux kernel is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical9.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.78%
Remediation
Version ranges on file
Affected products
Linux Kernel · cpe linux/linux kernel

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.)

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Linux Kernel3.1.0 → 5.10.259; 5.11.0 → 5.15.210; 5.16.0 → 6.1.176
  • cpe linux/linux kernel7.1
  • cpe linux/linux kernel< 5.10.259
  • cpe linux/linux kernel< 5.15.210
  • cpe linux/linux kernel< 6.1.176
  • cpe linux/linux kernel< 6.12.93
  • cpe linux/linux kernel< 6.18.35
  • cpe linux/linux kernel< 6.6.143
  • cpe linux/linux kernel< 7.0.12

How to fix CVE-2026-63887

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-63887. EPSS is 0.78%. Act only if a listed version of linux kernel is installed.

Which versions are affected?

Compare what you have installed with Kernel 3.1.0 → 5.10.259; 5.11.0 → 5.15.210; 5.16.0 → 6.1.176; linux/linux kernel 7.1; linux/linux kernel < 5.10.259; linux/linux kernel < 5.15.210. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-120: Classic Buffer Overflow; CWE-122: Heap-based Buffer Overflow. EPSS 0.78%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Jul 19, 2026 · NIST NVD

    Detected

    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

  2. Oct 22, 2026 · NIST NVD

    Updated

    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

  3. Oct 22, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    Kernel fixed in 5.10.259; Kernel fixed in 5.15.210; Kernel fixed in 6.1.176; Kernel fixed in 6.6.143

  4. Oct 22, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    Kernel fixed in 5.10.259; 5.11.0

  5. Oct 22, 2026 · OpenSSF OSV / OSV Scanner

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-63887

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-63887

    30-day exploitation probability 0.78%

    first.org
  • NIST NVDVulnerability recordCVE-2026-63887

    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 alloc

    nvd.nist.gov
  • OpenSSF OSV / OSV ScannerPackage advisoryCVE-2026-63887

    scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf

    osv.dev

References

Freshness

Last verified in this catalog Oct 23, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.