# CVE-2026-63888: scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

> A double-free and buffer overread in the Linux kernel iSCSI target allows remote attackers to cause denial of service or potentially execute code when DataDigest is enabled.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-63888, DEBIAN-CVE-2026-63888, GHSA-ww53-m8wh-v825, ROOT-OS-UBUNTU-2204-CVE-2026-63888, UBUNTU-CVE-2026-63888

## What is CVE-2026-63888?

CVE-2026-63888 is a critical use after free vulnerability in Linux kernel, published on 19 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

Two latent bugs in the Text-phase handler, both present since the
original LIO integration in commit e48354ce078c ("iscsi-target: Add
iSCSI fabric support for target v4.1"):

1) DataDigest CRC buffer overread (4 bytes past text_in).

   text_in is kzalloc()'d at ALIGN(payload_length, 4).  rx_size is then
   incremented by ISCSI_CRC_LEN to make room for the received DataDigest
   in the iovec, but the same (now-bumped) rx_size is passed as the
   buffer length to iscsit_crc_buf():

       if (conn->conn_ops->DataDigest) {
               ...
               rx_size += ISCSI_CRC_LEN;
       }
       ...
       if (conn->conn_ops->DataDigest) {
               data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);

   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so
   when DataDigest is negotiated it reads 4 bytes past the end of the
   text_in allocation.  KASAN reproduces this directly on the unpatched
   mainline tree as slab-out-of-bounds in crc32c() called from the Text
   PDU path.  The OOB bytes feed crc32c() and are then compared against
   the initiator-supplied checksum, so the value does not flow back to
   the attacker, but the kernel does read past the buffer on every Text
   PDU with DataDigest=CRC32C.

   Fix by passing the actual padded payload length
   (ALIGN(payload_length, 4)) that was used for the kzalloc().

2) Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest
   drop.

   On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler
   silently drops the PDU and lets the initiator plug the CmdSN gap:

               kfree(text_in);
               return 0;

   cmd->text_in_ptr still points at the freed buffer.  The next Text
   Request on the same ITT re-enters iscsit_setup_text_cmd(), which
   unconditionally does

       kfree(cmd->text_in_ptr);
       cmd->text_in_ptr = NULL;

   freeing the same pointer a second time.  Session teardown via
   iscsit_release_cmd() has the same shape and hits the same double-free
   if the connection is dropped before a second Text Request arrives.

   On an unmodified mainline tree the bug-1 CRC overread fires first on
   the initial valid Text Request and perturbs the subsequent state, so
   #4 was isolated by building a kernel with only the bug-1 hunk of this
   patch applied plus temporary printk() observability around the three
   relevant kfree() sites.  The observability prints are not part of
   this patch.  On that build, a three-PDU Text Request sequence after
   login produces two back-to-back splats:

       BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??
       BUG: KASAN: double-free in iscsit_release_cmd+0x??

   showing the same pointer freed in the ERL>0 drop path and again in
   iscsit_setup_text_cmd() (next Text Request on the same ITT) and once
   more in iscsit_release_cmd() (session teardown).  On distro kernels
   with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free
   becomes a remote kernel BUG(); on non-hardened kernels it corrupts
   the slab freelist.

   Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop
   path.  With both hunks applied #4 is directly observable on the stock
   tree without observability printks; fixing bug-1 alone would mask #4
   less, not more, so the hunks are submitted together.

Both fixes are one-liners.  The Text PDU state machine is unchanged and
the wire protocol is unaffected.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2026-63888?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-63888?

Apply the vendor's patch.

## Is CVE-2026-63888 being exploited?

There is no known exploitation of CVE-2026-63888 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63888 and fix it if it is affected.

What it is: CVE-2026-63888 is a critical use after free vulnerability in Linux kernel, published on 19 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-63888 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-63888/ (Markdown: https://insights.sbomify.com/CVE-2026-63888/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63888
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63888
- OSV: https://osv.dev/vulnerability/CVE-2026-63888

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63888/
Summaries are generated and may contain mistakes; the official description above is the record.