# CVE-2021-47636: linux: In the Linux kernel, the following vulnerability has been resolved:  ubifs: Fix read out-of-bounds in ubifs_wbuf_writ...

CVE-2021-47636 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47636, released February 26, 2025. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-47636
- Priority: High
- CVSS: 7.1 (high)
- EPSS: 0.0026
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 26, 2025

## Description

In the Linux kernel, the following vulnerability has been resolved:  ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()  Function ubifs_wbuf_write_nolock() may access buf out of bounds in following process:  ubifs_wbuf_write_nolock():   aligned_len = ALIGN(len, 8);   // Assume len = 4089, aligned_len = 4096   if (aligned_len <= wbuf->avail) ... // Not satisfy   if (wbuf->used) {     ubifs_leb_write()  // Fill some data in avail wbuf     len -= wbuf->avail;   // len is still not 8-bytes aligned     aligned_len -= wbuf->avail;   }   n = aligned_len >> c->max_write_shift;   if (n) {     n <<= c->max_write_shift;     err = ubifs_leb_write(c, wbuf->lnum, buf + written,                           wbuf->offs, n);     // n > len, read out of bounds less than 8(n-len) bytes   }  , which can be catched by KASAN:   =========================================================   BUG: KASAN: slab-out-of-bounds in ecc_sw_hamming_calculate+0x1dc/0x7d0   Read of size 4 at addr ffff888105594ff8 by task kworker/u8:4/128   Workqueue: writeback wb_workfn (flush-ubifs_0_0)   Call Trace:     kasan_report.cold+0x81/0x165     nand_write_page_swecc+0xa9/0x160     ubifs_leb_write+0xf2/0x1b0 [ubifs]     ubifs_wbuf_write_nolock+0x421/0x12c0 [ubifs]     write_head+0xdc/0x1c0 [ubifs]     ubifs_jnl_write_inode+0x627/0x960 [ubifs]     wb_workfn+0x8af/0xb80  Function ubifs_wbuf_write_nolock() accepts that parameter 'len' is not 8 bytes aligned, the 'len' represents the true length of buf (which is allocated in 'ubifs_jnl_xxx', eg. ubifs_jnl_write_inode), so ubifs_wbuf_write_nolock() must handle the length read from 'buf' carefully to write leb safely.  Fetch a reproducer in [Link].

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.17.3-1 | [DEBIAN-CVE-2021-47636](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47636.md) | Feb 26, 2025 |
| Linux | linux Debian 13.5 (trixie) | 5.17.3-1 | [DEBIAN-CVE-2021-47636](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47636.md) | Feb 26, 2025 |
| Linux | linux Debian 14 | 5.17.3-1 | [DEBIAN-CVE-2021-47636](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47636.md) | Feb 26, 2025 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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