A recently discovered vulnerability, dubbed CVE-2025-25724, has been identified in the list_item_verbose function, a part of libarchive's tar/util.c. This vulnerability could potentially lead to a denial of service or other unspecified impacts, due to improper handling of strftime return values when processing a specially crafted TAR archive with a verbose value of 2. Specifically, this issue arises when the 100-byte buffer used in the function does not suffice for a custom locale.

In this blog post, we will dive into the technical details surrounding this vulnerability, discuss the consequences it may have, provide a code snippet illustrating the issue, and offer some advice on how to safeguard against this kind of exploit.

Vulnerability Analysis

The vulnerable code in libarchive's tar/util.c can be found in the list_item_verbose function. Here is a code snippet that showcases the issue:

static void
list_item_verbose(struct archive_read *a, struct archive_entry *entry)
{
    //...
    char                    strtime[100];
    //...
    const struct tm *tm = archive_entry_mtime(entry);

    /* Create the formatted timestamp string */
    strftime(strtime, sizeof(strtime), "%F %T", tm);
    //...
}

In the code snippet above, the strftime function is called to format the timestamp associated with an entry in the TAR archive. The function takes three arguments: a character buffer strtime with a size of 100 bytes, the maximum size sizeof(strtime) of the buffer, and a format string.

The issue arises due to the lack of error handling for the strftime function call. strftime returns if the resulting string buffer is insufficient to hold the output. In case a custom locale is being used, the 100-byte buffer might not be sufficient to hold the resulting time string, leading to a buffer overflow. This could trigger a denial of service or have other unspecified impacts on the affected system.

A possible exploit for this vulnerability would require an attacker to craft a TAR archive with a verbose value of 2 and use a custom locale that causes the buffer overflow in the list_item_verbose function. When such a TAR archive is processed, it would exploit the vulnerable code, leading to the undesirable outcomes mentioned earlier.

The Common Vulnerabilities and Exposures (CVE®) identifier for this vulnerability is CVE-2025-25724.

For more details on this vulnerability, please refer to the following resources

1. libarchive GitHub Repository – The official GitHub repository for the libarchive project.
2. CVE-2025-25724 Details – The official MITRE description of the CVE identifier for this vulnerability.

Mitigation and Remediation

The vulnerability affects libarchive versions up to and including 3.7.7. Users of libarchive are encouraged to upgrade to the latest release in order to avoid potential exploits resulting from this vulnerability. Additionally, developers can implement proper error handling for the strftime function call in the affected code, e.g.,

size_t ret = strftime(strtime, sizeof(strtime), "%F %T", tm);
if (ret == ) {
    // Handle error
}

By checking the return value of strftime and taking appropriate action in the event of a failure, developers can ensure that the vulnerability is addressed and effectively mitigated.

Conclusion

In summary, CVE-2025-25724 is a critical vulnerability in libarchive that results from improper handling of strftime return values in the list_item_verbose function in tar/util.c. This issue could potentially lead to denial of service or other unspecified impacts when processing a specially crafted TAR archive with a verbose value of 2. Users and developers running versions up to and including 3.7.7 are advised to update to the latest version of libarchive and implement proper error handling for the strftime function call in order to protect against this exploit.

Timeline

Published on: 03/02/2025 02:15:36 UTC