CVE-2026-40494: SAIL Library Buffer Overflow Vulnerability

CVE-2026-40494 Overview

A critical heap buffer overflow vulnerability has been discovered in SAIL, a cross-platform library for loading and saving images with support for animation, metadata, and ICC profiles. The vulnerability exists in the TGA codec's RLE (Run-Length Encoding) decoder within tga.c, where an asymmetric bounds check allows attackers to write up to 496 bytes of attacker-controlled data past the end of a heap buffer.

Critical Impact

This heap buffer overflow vulnerability can be exploited remotely without authentication, potentially allowing attackers to execute arbitrary code, cause denial of service, or compromise system integrity through maliciously crafted TGA image files.

Affected Products

• SAIL library versions prior to commit 45d48d1f2e8e0d73e80bc1fd5310cb57f4547302
• Applications utilizing the SAIL library's TGA codec functionality
• Systems processing untrusted TGA image files through SAIL

Discovery Timeline

• 2026-04-18 - CVE CVE-2026-40494 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2026-40494

Vulnerability Analysis

The vulnerability resides in the TGA codec's RLE decoder implementation within the tga.c source file. The core issue stems from an asymmetric bounds checking pattern between two code paths handling different packet types in the RLE decompression routine.

The run-packet path (line 297) correctly implements bounds checking by clamping the repeat count to the remaining buffer space, preventing buffer overflows when processing run-length encoded sequences. However, the raw-packet path (lines 305-311) lacks an equivalent bounds check, creating a critical security gap.

This asymmetry allows an attacker to craft a malicious TGA file that triggers the raw-packet code path with a packet count that exceeds the remaining buffer capacity. Since the vulnerability is network-accessible and requires no privileges or user interaction, attackers can deliver malicious TGA images through various vectors including web applications, email attachments, or file uploads.

Root Cause

The root cause is classified under CWE-787 (Out-of-bounds Write). The vulnerability originates from inconsistent input validation between two parallel code paths in the RLE decoder. While the developer correctly implemented bounds checking for run-length packets, the raw packet handling code was left without equivalent protection, allowing unconstrained writes up to 496 bytes beyond the allocated heap buffer boundary.

Attack Vector

The attack vector is network-based, allowing remote exploitation without authentication. An attacker can craft a malicious TGA image file with specially constructed RLE packet data that exploits the missing bounds check in the raw-packet path. When the vulnerable SAIL library processes this malicious image, the out-of-bounds write occurs on the heap, potentially enabling:

1. Heap corruption leading to arbitrary code execution
2. Control flow hijacking by overwriting function pointers or metadata
3. Denial of service through memory corruption crashes

             unsigned char marker;
             SAIL_TRY(tga_state->io->strict_read(tga_state->io->stream, &marker, 1));
 
-            unsigned count = (marker & 0x7F) + 1;
+            const unsigned packet_count = (marker & 0x7F) + 1;
+            const unsigned remaining    = pixels_num - i;
 
             /* 7th bit set = RLE packet. */
             if (marker & 0x80)

Source: GitHub Commit Update

The patch introduces proper bounds tracking by calculating the remaining pixels in the buffer and using packet_count consistently across both code paths.

Detection Methods for CVE-2026-40494

Indicators of Compromise

• Malformed TGA image files with abnormal RLE packet structures designed to trigger buffer overflows
• Application crashes or unexpected termination when processing TGA files through SAIL library
• Memory corruption signatures in crash dumps showing heap overflow patterns near TGA decoding functions
• Unusual process behavior following TGA file processing, including unexpected network connections or file system activity

Detection Strategies

• Deploy file integrity monitoring to detect modifications to SAIL library binaries and dependent applications
• Implement input validation for TGA files at application boundaries, checking for malformed RLE packet structures
• Monitor for crash patterns in applications utilizing SAIL library TGA processing functionality
• Enable heap protection mechanisms (ASLR, stack canaries, heap guards) to detect exploitation attempts

Monitoring Recommendations

• Log and analyze all TGA file processing events in applications using the SAIL library
• Implement anomaly detection for unusual memory allocation patterns during image processing
• Deploy endpoint detection and response (EDR) solutions capable of detecting heap corruption exploitation techniques
• Monitor application error logs for segmentation faults or access violations related to image processing

How to Mitigate CVE-2026-40494

Immediate Actions Required

• Update the SAIL library to include commit 45d48d1f2e8e0d73e80bc1fd5310cb57f4547302 or later immediately
• Audit all applications using SAIL library to identify those processing untrusted TGA files
• Implement input filtering to block or quarantine TGA files from untrusted sources pending patch deployment
• Enable heap exploitation mitigations such as ASLR and DEP on systems running vulnerable versions

Patch Information

The vulnerability has been fixed in commit 45d48d1f2e8e0d73e80bc1fd5310cb57f4547302. The patch introduces proper bounds checking for the raw-packet path by calculating the remaining buffer space and ensuring packet counts do not exceed available capacity. Organizations should update to a version of SAIL that includes this commit. For detailed patch information, see the GitHub Security Advisory GHSA-cp2j-rwh4-r46f.

Workarounds

• Disable TGA file processing in applications where it is not required until patches can be applied
• Implement strict file type validation and reject TGA files at application entry points from untrusted sources
• Deploy web application firewalls (WAF) with rules to inspect and block malicious TGA file uploads
• Isolate image processing workloads in sandboxed environments to limit the impact of successful exploitation

# Configuration example - Disable TGA codec loading in SAIL (if supported)
# Check application documentation for specific configuration options
# Example: Restrict file types processed by application
export SAIL_DISABLED_CODECS="tga"

# Alternative: Use file type validation at upload point
file --mime-type uploaded_image | grep -v "image/x-tga" || reject_file