CyberSecBulletin
CVE-2023-52973NVD status: Analyzed

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2023-52973 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions af79ea9a2443016f64d8fd8d72020cc874f0e066, 6332f52f44b9776568bf3c0b714ddfb0bb175e78, d0332cbf53dad06a22189cc341391237f4ea6d9f as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to af79ea9a2443016f64d8fd8d72020cc874f0e066 or 6332f52f44b9776568bf3c0b714ddfb0bb175e78 or d0332cbf53dad06a22189cc341391237f4ea6d9f or 55515d7d8743b71b80bfe68e89eb9d92630626ab, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 4.14.329 or 4.19.273 or 5.4.232 or 5.10.168, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, af79ea9a2443016f64d8fd8d72020cc874f0e066; ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, 6332f52f44b9776568bf3c0b714ddfb0bb175e78; ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, d0332cbf53dad06a22189cc341391237f4ea6d9f; ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, 55515d7d8743b71b80bfe68e89eb9d92630626ab; ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, fc9e27f3ba083534b8bbf72ab0f5c810ffdc7d18; ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, 8506f16aae9daf354e3732bcfd447e2a97f023df; ac751efa6a0d70f2c9daef5c7e3a92270f5c2dff up to, but not including, 226fae124b2dac217ea5436060d623ff3385bc34; 2.6.38af79ea9a2443016f64d8fd8d72020cc874f0e066, 6332f52f44b9776568bf3c0b714ddfb0bb175e78, d0332cbf53dad06a22189cc341391237f4ea6d9f, 55515d7d8743b71b80bfe68e89eb9d92630626ab, fc9e27f3ba083534b8bbf72ab0f5c810ffdc7d18, 8506f16aae9daf354e3732bcfd447e2a97f023df
LinuxLinux Kernel2.6.38 up to, but not including, 4.14.329; 4.15 up to, but not including, 4.19.273; 4.20 up to, but not including, 5.4.232; 5.5 up to, but not including, 5.10.168; 5.11 up to, but not including, 5.15.93; 5.16 up to, but not including, 6.1.11; 6.24.14.329, 4.19.273, 5.4.232, 5.10.168, 5.15.93, 6.1.11

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).

Official description

In the Linux kernel, the following vulnerability has been resolved: vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF After a call to console_unlock() in vcs_read() the vc_data struct can be freed by vc_deallocate(). Because of that, the struct vc_data pointer load must be done at the top of while loop in vcs_read() to avoid a UAF when vcs_size() is called. Syzkaller reported a UAF in vcs_size(). BUG: KASAN: use-after-free in vcs_size (drivers/tty/vt/vc_screen.c:215) Read of size 4 at addr ffff8881137479a8 by task 4a005ed81e27e65/1537 CPU: 0 PID: 1537 Comm: 4a005ed81e27e65 Not tainted 6.2.0-rc5 #1 Hardware name: Red Hat KVM, BIOS 1.15.0-2.module Call Trace: <TASK> __asan_report_load4_noabort (mm/kasan/report_generic.c:350) vcs_size (drivers/tty/vt/vc_screen.c:215) vcs_read (drivers/tty/vt/vc_screen.c:415) vfs_read (fs/read_write.c:468 fs/read_write.c:450) ... </TASK> Allocated by task 1191: ... kmalloc_trace (mm/slab_common.c:1069) vc_allocate (./include/linux/slab.h:580 ./include/linux/slab.h:720 drivers/tty/vt/vt.c:1128 drivers/tty/vt/vt.c:1108) con_install (drivers/tty/vt/vt.c:3383) tty_init_dev (drivers/tty/tty_io.c:1301 drivers/tty/tty_io.c:1413 drivers/tty/tty_io.c:1390) tty_open (drivers/tty/tty_io.c:2080 drivers/tty/tty_io.c:2126) chrdev_open (fs/char_dev.c:415) do_dentry_open (fs/open.c:883) vfs_open (fs/open.c:1014) ... Freed by task 1548: ... kfree (mm/slab_common.c:1021) vc_port_destruct (drivers/tty/vt/vt.c:1094) tty_port_destructor (drivers/tty/tty_port.c:296) tty_port_put (drivers/tty/tty_port.c:312) vt_disallocate_all (drivers/tty/vt/vt_ioctl.c:662 (discriminator 2)) vt_ioctl (drivers/tty/vt/vt_ioctl.c:903) tty_ioctl (drivers/tty/tty_io.c:2776) ... The buggy address belongs to the object at ffff888113747800 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 424 bytes inside of 1024-byte region [ffff888113747800, ffff888113747c00) The buggy address belongs to the physical page: page:00000000b3fe6c7c refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x113740 head:00000000b3fe6c7c order:3 compound_mapcount:0 subpages_mapcount:0 compound_pincount:0 anon flags: 0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff) raw: 0017ffffc0010200 ffff888100042dc0 0000000000000000 dead000000000001 raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888113747880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888113747900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff888113747980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888113747a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888113747a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== Disabling lock debugging due to kernel taint

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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