CVE-2025-3409: Nothings Stb Image.h Buffer Overflow Flaw

CVE-2025-3409 Overview

CVE-2025-3409 is a stack-based buffer overflow vulnerability in the Nothings stb library, a widely used collection of single-file public domain C/C++ libraries. The flaw resides in the stb_include_string function and is triggered through manipulation of the path_to_includes argument. An attacker can initiate the attack remotely when an application passes untrusted input to the affected function. The stb project does not use formal versioning, so affected and unaffected releases cannot be enumerated; the issue was reported against commit f056911. The vendor was contacted prior to disclosure but did not respond. This vulnerability is classified under CWE-119, improper restriction of operations within the bounds of a memory buffer.

Critical Impact

A remote attacker controlling the path_to_includes argument can overflow a stack buffer in stb_include_string, leading to memory corruption and potential code execution within the host application.

Affected Products

• Nothings stb_image.h (commit f056911 and prior)
• Applications statically linking the stb_include helper from the stb single-file library collection
• Downstream projects bundling vulnerable copies of stb without versioning metadata

Discovery Timeline

• 2025-04-08 - CVE-2025-3409 published to NVD
• 2025-10-16 - Last updated in NVD database

Technical Details for CVE-2025-3409

Vulnerability Analysis

The stb library bundles small utility helpers, including stb_include_string, which performs C-like #include expansion on text passed to it. The function accepts a path_to_includes argument describing where included files reside. The implementation copies this path into a fixed-size stack buffer without enforcing the destination length. When path_to_includes exceeds the buffer capacity, adjacent stack memory is overwritten, corrupting saved registers, frame pointers, and return addresses.

Because the function is invoked by applications that may accept include paths from network input, configuration files, or scripted asset pipelines, the attack surface extends beyond local-only use cases. Successful exploitation depends on the calling application's compilation flags and platform mitigations such as stack canaries, ASLR, and non-executable stacks.

Root Cause

The root cause is missing bounds enforcement when concatenating or copying the caller-supplied path_to_includes string into a stack-allocated buffer inside stb_include_string. The function trusts the caller to provide a length-bounded input, which is unsafe for any library exposed to attacker-controlled data.

Attack Vector

Exploitation requires the attacker to influence the path_to_includes value passed to stb_include_string. In many integrations, this occurs through asset preprocessing, shader includes, or build-time tooling that accepts paths from user-supplied content. Exploitation requires user interaction in many deployment models, since the vulnerable function is typically triggered during content loading.

No public proof-of-concept exploit is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The current EPSS probability is 0.246%.

No verified exploitation code is publicly available. See the VulDB entry for CVE-2025-3409 for additional technical detail.

Detection Methods for CVE-2025-3409

Indicators of Compromise

• Unexpected crashes or segmentation faults in processes that load assets through stb_include_string
• Core dumps showing corrupted return addresses or stack canary violations originating in stb helper code
• Unusually long path strings observed in asset pipelines, shader includes, or build logs

Detection Strategies

• Inventory binaries and source trees for embedded copies of stb_include.h or stb.h at or before commit f056911
• Apply static analysis to flag unbounded strcpy, strcat, or sprintf calls operating on stack buffers within bundled stb helpers
• Enable AddressSanitizer or stack-protector instrumentation during fuzz testing of any consumer of stb_include_string

Monitoring Recommendations

• Monitor application crash telemetry and Windows Error Reporting or Linux coredump events for processes that parse include directives
• Alert on abnormal child-process creation from applications that embed stb, indicating possible post-exploitation activity
• Capture and review path arguments passed to asset preprocessing tools, especially those sourced from network or user input

How to Mitigate CVE-2025-3409

Immediate Actions Required

• Identify every project consuming stb_include.h and audit how path_to_includes is supplied to stb_include_string
• Reject or truncate caller-supplied include paths to a safe maximum length before invoking the function
• Rebuild affected applications with stack protection (-fstack-protector-strong), ASLR, and non-executable stack enforcement

Patch Information

No official upstream patch has been published. The maintainer did not respond to disclosure outreach. Consumers should pull the latest stb commit from the upstream repository and verify whether stb_include_string has been hardened, or apply local patches to bound the path copy.

Workarounds

• Wrap calls to stb_include_string with input validation that enforces a strict maximum length on path_to_includes
• Replace stb_include_string with a custom include resolver that uses bounded string APIs such as snprintf or strncpy_s
• Sandbox processes that perform asset preprocessing using seccomp, AppArmor, or equivalent OS-level isolation to limit blast radius

# Configuration example: enforce stack hardening when building consumers of stb
gcc -O2 -D_FORTIFY_SOURCE=2 -fstack-protector-strong \
    -fPIE -pie -Wl,-z,noexecstack -Wl,-z,relro,-z,now \
    -o myapp myapp.c