CVE-2025-4878: Uninitialized Variable in libssh Leads to Potential Signing Failures or Heap Corruption
This post discusses a recently discovered vulnerability, CVE-2025-4878, affecting the libssh library. This flaw, stemming from an uninitialized variable, can lead to security issues under specific circumstances. Let's dive into the details.
Vulnerability Details
- CVE ID: CVE-2025-4878
- Description: A vulnerability was found in libssh, where an uninitialized variable exists under certain conditions in the
privatekey_from_file()function. This flaw can be triggered if the file specified by the filename doesn't exist and may lead to possible signing failures or heap corruption. - CVSS Score and Vector:
- CVSS 3.1 Score: 3.6 (LOW)
- CVSS 3.1 Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N
- Explanation: This vulnerability has a low severity rating. It requires local access and a high attack complexity, meaning specific conditions must be met for successful exploitation. A low-privileged user is needed, and there's no user interaction. The impact is limited to low confidentiality and integrity, with no availability impact.
- Exploit Requirements: The file specified in
privatekey_from_file()must not exist. A local attacker needs low privileges. - Affected Vendor, Product, Version: libssh (version information unavailable).
- CWE:
- CWE-416: Use After Free
- Explanation: A "Use After Free" condition occurs when a program attempts to use memory after it has been freed. This can lead to crashes, arbitrary code execution, or other unexpected behavior. In the context of libssh, the uninitialized variable may lead to a use-after-free scenario if the program attempts to operate on that memory region, post a failed file read attempt.
Timeline of Events
- 2025-07-22: CVE ID assigned and vulnerability reported.
Exploitability & Real-World Risk
While the CVSS score is low, the risk shouldn't be completely dismissed. If an attacker can control the filename passed to privatekey_from_file() and ensure it doesn't exist, they could potentially trigger the uninitialized variable condition. The real-world impact depends on how libssh is used in applications. A successful exploit could lead to unpredictable behavior, including denial of service due to heap corruption or, in more severe cases, compromise of cryptographic keys.
Recommendations
- Apply Patches: Keep libssh updated with the latest patches released by the maintainers.
- Input Validation: Ensure proper validation of filenames passed to
privatekey_from_file()to prevent attackers from controlling the input. - Error Handling: Implement robust error handling to gracefully manage file access failures.
Technical Insight
The vulnerability arises because, under specific conditions, the variable isn't properly initialized before being used. Specifically, if the specified filename doesn't exist, the variable may retain an indeterminate value. Subsequent operations on this uninitialized variable could lead to unpredictable program behavior and potentially compromise security.
Credit to Researcher(s)
Credit to Red Hat Security Team for discovering and reporting this vulnerability.
References
Tags
#libssh #CVE-2025-4878 #UninitializedVariable #HeapCorruption #SigningFailure #SecurityVulnerability
Summary: CVE-2025-4878 details an uninitialized variable vulnerability in libssh's privatekey_from_file() function. When a file doesn't exist, this can lead to signing failures or heap corruption. Apply patches and validate inputs.
CVE ID: CVE-2025-4878
Risk Analysis: Successful exploitation can lead to unpredictable program behavior, potentially including denial of service or compromise of cryptographic keys.
Recommendation: Apply the latest patches for libssh, validate filenames passed to privatekey_from_file(), and implement robust error handling for file access failures.
Timeline
- 2025-07-22: CVE ID assigned and vulnerability reported.