{"id":48671,"date":"2025-06-04T00:09:12","date_gmt":"2025-06-04T00:09:12","guid":{"rendered":""},"modified":"2025-08-30T00:12:42","modified_gmt":"2025-08-30T06:12:42","slug":"cve-2025-21879-the-linux-kernel-btrfs-use-after-free-vulnerability","status":"publish","type":"post","link":"https:\/\/www.ameeba.com\/blog\/cve-2025-21879-the-linux-kernel-btrfs-use-after-free-vulnerability\/","title":{"rendered":"CVE-2025-21879: The Linux Kernel Btrfs Use-After-Free Vulnerability<\/strong>"},"content":{"rendered":"

Overview<\/strong><\/p>\n

CVE-2025-21879 is a significant vulnerability found in the Linux kernel, specifically in the btrfs file system. This vulnerability arises from a use-after-free condition on an inode when scanning root during em shrinking. The impact of this vulnerability is critical<\/a> as it potentially allows malicious actors to compromise the system or cause data leakage. It matters because the Linux kernel<\/a> is widely used in various products and systems, from servers and desktops to embedded systems, making a large number of devices potentially vulnerable to this exploit.<\/p>\n

Vulnerability Summary<\/strong><\/p>\n

CVE ID: CVE-2025-21879
\nSeverity: High (7.8 CVSS Score)
\nAttack Vector: Local
\nPrivileges Required: Low
\nUser Interaction: None
\nImpact: Compromise of system integrity, potential data leakage<\/a><\/p>\n

Affected Products<\/strong><\/p>\n

Product | Affected Versions<\/p>\n

Linux kernel<\/a> | Versions using btrfs filesystem<\/p>\n

How the Exploit Works<\/strong><\/p>\n

The exploit takes advantage of a use-after-free condition in the Linux kernel’s btrfs file system<\/a>. Specifically, the btrfs_scan_root() function is accessing the inode’s root<\/a> (and fs_info) in a call to btrfs_fs_closing() after the inode has been scheduled for a delayed iput. If the cleaner kthread completes the iput before the inode is dereferenced in the call to btrfs_fs_closing(), it can result in a use-after-free<\/a> on the inode. This situation can be exploited by an attacker to potentially compromise the system<\/a> or cause data leakage.<\/p>\n

Conceptual Example Code<\/strong><\/p>\n

Below is a conceptual example demonstrating how an attacker might exploit<\/a> this vulnerability. Here, the attacker triggers the vulnerable condition<\/a> by causing a delayed iput on the inode and then leveraging the resulting use-after-free condition.<\/p>\n

\/\/ Create a delayed iput on the inode\ntrigger_delayed_iput(inode);\n\/\/ Then, trigger the use-after-free condition\naccess_inode_after_free(inode);<\/code><\/pre>\n
In real-world attacks, the actual code would be much more complex and would involve specific techniques to exploit the use-after-free condition effectively.<\/p>\n
Mitigation Guidance<\/strong><\/p>\n
To mitigate this vulnerability, users are advised to apply the vendor patch as soon as it is available. If the patch cannot be applied immediately, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can provide temporary mitigation. However, these measures do not entirely resolve the vulnerability and only limit the potential<\/a> for exploitation. Therefore, applying the vendor patch remains the most effective way to secure your systems against this vulnerability<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
Overview CVE-2025-21879 is a significant vulnerability found in the Linux kernel, specifically in the btrfs file system. This vulnerability arises from a use-after-free condition on an inode when scanning root during em shrinking. The impact of this vulnerability is critical as it potentially allows malicious actors to compromise the system or cause data leakage. It […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[1],"tags":[],"vendor":[88],"product":[95],"attack_vector":[],"asset_type":[],"severity":[],"exploit_status":[],"class_list":["post-48671","post","type-post","status-publish","format-standard","hentry","category-uncategorized","vendor-linux","product-linux-kernel"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t