CVE-2026-8454: Tonyc Imager Buffer Overflow Vulnerability

CVE-2026-8454 Overview

CVE-2026-8454 is a heap out-of-bounds write vulnerability in Imager::File::GIF versions through 1.002 for Perl. The flaw resides in the i_readgif_multi_low function, which allocates a single per-row GifRow buffer sized to the GIF's global screen width (SWidth) and reuses it across every image frame in the file. While the page-match branch validates Image.Width + Image.Left > SWidth before each DGifGetLine write, the parallel skip-image branch at imgif.c:790-805 performs no such bounds check. Attackers can craft multi-frame GIF files that trigger the unchecked write path, corrupting heap memory during image decoding [CWE-787].

Critical Impact

Processing a crafted multi-frame GIF in any Perl application using Imager::File::GIF causes a heap out-of-bounds write, potentially leading to memory corruption, crashes, or arbitrary code execution.

Affected Products

• Tonyc Imager::File::GIF for Perl, all versions through 1.002
• Perl applications that consume untrusted GIF input via the Imager module
• Downstream Linux distributions packaging Imager-File-GIF ≤ 1.002

Discovery Timeline

• 2026-05-15 - Vulnerability disclosed via OpenWall oss-security mailing list
• 2026-05-15 - CVE-2026-8454 published to NVD
• 2026-05-18 - Last updated in NVD database

Technical Details for CVE-2026-8454

Vulnerability Analysis

The vulnerability resides in i_readgif_multi_low inside imgif.c, the core multi-frame GIF reader for Imager::File::GIF. The function allocates one GifRow buffer of length SWidth (the GIF global screen width) once and reuses it for every embedded image. Each sub-image within a GIF can declare its own Image.Width and Image.Left offsets in its local image descriptor. When a frame's Image.Width + Image.Left exceeds SWidth, writing a row of that frame into GifRow overflows the heap allocation.

Root Cause

The page-match decoding branch correctly checks Image.Width + Image.Left > SWidth and rejects frames that would write past the buffer. The parallel skip-image branch at imgif.c:790-805 calls DGifGetLine(GifFile, GifRow, Width) using the attacker-controlled local Width value without performing the equivalent validation. This inconsistency between the two code paths allows oversized rows to be written into a fixed-size heap buffer [CWE-787].

Attack Vector

Exploitation requires the victim to open or otherwise process a malicious GIF file with an application that uses Imager::File::GIF. The attacker crafts a multi-frame GIF whose secondary frames declare Width and Left values that sum beyond the file's declared SWidth. When the decoder reaches the skip-image branch, DGifGetLine writes beyond GifRow, corrupting adjacent heap memory. User interaction is required to supply the malicious file.

+Imager-File-GIF 1.003
+=====================
+
+ - fix a buffer overflow when reading images
+   CVE-2026-8454
+
 Imager-File-GIF 1.002
 =====================

Source: GitHub Patch Commit

The upstream patch adds the missing width and offset validation to the skip-image branch, aligning it with the page-match branch.

Detection Methods for CVE-2026-8454

Indicators of Compromise

• Perl processes linking Imager::File::GIF crashing with SIGSEGV or glibc heap corruption messages such as malloc(): corrupted chunk while parsing GIF input
• GIF files where sub-image local descriptors declare Image.Width + Image.Left greater than the file's Logical Screen Width
• Unexpected child process termination in image-processing pipelines (CMS uploads, thumbnailers, mail filters) when handling user-supplied GIFs

Detection Strategies

• Inspect installed Perl module versions and flag any host with Imager::File::GIF ≤ 1.002 using cpan -D Imager::File::GIF or distribution package queries
• Statically scan inbound GIF files for malformed frame geometry by parsing the Logical Screen Descriptor and each Image Descriptor before passing them to vulnerable decoders
• Monitor application logs and core dumps from web services, mail gateways, and batch jobs that process attacker-controlled GIFs

Monitoring Recommendations

• Forward Perl application crash telemetry and coredumpctl events into a centralized log platform for correlation against image upload activity
• Track outbound network connections initiated by image-processing workers immediately after GIF parsing to surface post-exploitation behavior
• Alert on repeated GIF parse failures from a single source, which can indicate fuzzing or exploit reconnaissance

How to Mitigate CVE-2026-8454

Immediate Actions Required

• Upgrade Imager::File::GIF to version 1.003 or later on every host that runs Perl-based image processing
• Audit dependent applications (web apps, mailers, asset pipelines) for direct or transitive use of Imager::File::GIF and schedule restarts after upgrade
• Until patching completes, reject or pre-validate untrusted GIF uploads using a standalone parser that enforces Image.Width + Image.Left <= SWidth

Patch Information

The vendor fixed the issue in Imager-File-GIF 1.003, released alongside Imager 1.030 on 13 Apr 2026. The fix commit 782e9c06cc75a0f7eed383f39522f51f44598b04 adds bounds validation to the skip-image branch in imgif.c. See the GitHub Patch Commit and the MetaCPAN Release Changes for details. Additional context is available in the OpenWall OSS-Security Post.

Workarounds

• Disable GIF processing in Imager workflows where feasible by restricting accepted formats to PNG or JPEG until the patched module is deployed
• Sandbox Perl image-processing workers with seccomp, AppArmor, or container isolation to limit the impact of heap corruption
• Pre-filter GIF inputs through a hardened tool such as ImageMagick with strict policy.xml limits before handing files to Imager

# Upgrade Imager::File::GIF to the patched release
cpanm Imager::File::GIF@1.003

# Verify the installed version
perl -MImager::File::GIF -e 'print $Imager::File::GIF::VERSION, "\n"'