GNU sed up to 4.9 open_next_file toctou

Summaryinfo

A vulnerability classified as problematic has been found in GNU sed up to 4.9. This impacts the function open_next_file. The manipulation leads to toctou. This vulnerability is documented as CVE-2026-5958. The attack needs to be performed locally. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in GNU sed up to 4.9. This issue affects the function open_next_file. The manipulation with an unknown input leads to a toctou vulnerability. Using CWE to declare the problem leads to CWE-367. The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state. Impacted is integrity. The summary by CVE is:

When sed is invoked with both -i (in-place edit) and --follow-symlinks, the function open_next_file() performs two separate, non-atomic filesystem operations on the same path: 1. resolves symlink to its target and stores the resolved path for determining when output is written, 2. opens the original symlink path (not the resolved one) to read the file. Between these two calls there is a race window. If an attacker atomically replaces the symlink with a different target during that window, sed will: read content from the new (attacker-chosen) symlink target and write the processed result to the path recorded in step 1. This can lead to arbitrary file overwrite with attacker-controlled content in the context of the sed process. This issue was fixed in version 4.10.

The weakness was released with AFINE Team. The advisory is shared at gnu.org. The identification of this vulnerability is CVE-2026-5958 since 04/09/2026. The exploitation is known to be difficult. An attack has to be approached locally. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 313651 (SUSE SLES12 Security Update : sed (SUSE-SU-2026:1699-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 4.10 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (313651) and EUVD (EUVD-2026-23834). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Vendor

• GNU

Name

• sed

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7
• 4.8
• 4.9

License

• open-source

Website

• Vendor: https://www.gnu.org/

CPE 2.3info

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CPE 2.2info

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Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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