CVE-2026-49271: libheif Buffer Overflow Vulnerability

CVE-2026-49271 Overview

CVE-2026-49271 is an out-of-bounds read vulnerability in libheif, an open-source HEIF and AVIF file format decoder and encoder maintained by Struktur AG. The flaw affects the uncompressed HEIF decoder, which validates explicit icef compressed-unit offsets using the expression unit_offset + unit_size. Because this addition can wrap around due to integer overflow, a crafted HEIF file can bypass the range check. The decoder then constructs a vector from iterators pointing outside the compressed item buffer, triggering a heap-based out-of-bounds read [CWE-125] and process crash. Version 1.22.1 patches the issue.

Critical Impact
A maliciously crafted HEIF file can crash any application or service that parses untrusted HEIF input through libheif, resulting in denial of service.

Affected Products

libheif versions prior to 1.22.1
Applications and services that embed libheif for HEIF/AVIF decoding
Image processing pipelines accepting user-supplied HEIF files

Discovery Timeline

2026-06-19 - CVE-2026-49271 published to NVD
2026-06-23 - Last updated in NVD database

Technical Details for CVE-2026-49271

Vulnerability Analysis

The vulnerability resides in the uncompressed HEIF decoder path of libheif. The decoder reads icef (item compressed extent) metadata, which describes the offset and size of compressed units within an item buffer. Before accessing each unit, the decoder verifies that the unit falls within the buffer by computing unit_offset + unit_size and comparing the result against the buffer length.

The addition of two attacker-controlled values is not checked for arithmetic overflow. When the sum wraps around the integer range, the result becomes a small value that passes the bounds check. The decoder then treats the unit as valid and constructs an internal vector using iterators derived from unit_offset and unit_size. Those iterators reference memory outside the compressed item buffer, producing a heap out-of-bounds read and an immediate crash.

Root Cause

The root cause is missing integer overflow validation in the bounds-check logic. The decoder relies on a single additive comparison instead of verifying each operand independently or using a checked-addition helper. This is a classic instance of [CWE-125] Out-of-Bounds Read enabled by an unchecked arithmetic operation.

Attack Vector

Exploitation requires the victim to open or process a crafted HEIF file through an application linked against a vulnerable libheif build. The attack vector is network-reachable wherever HEIF files are accepted, including email attachments, web uploads, messaging clients, and cloud thumbnail generators. User interaction is required to trigger the parser. The impact is limited to availability — the flaw produces a read primitive that crashes the host process and does not expose confidentiality or integrity.

No public proof-of-concept exploit code is available in the references at this time. See the GitHub Security Advisory for additional technical details.

Detection Methods for CVE-2026-49271

Indicators of Compromise

Repeated crashes or segmentation faults in processes that invoke libheif, such as image thumbnailers, web servers, and media converters
Inbound HEIF or AVIF files from untrusted senders that trigger parser termination
Core dumps referencing libheif symbols in the UncompressedImageCodec or icef parsing paths

Detection Strategies

Inventory all software linked against libheif and compare installed versions against the 1.22.1 fix baseline
Hunt for crash telemetry on hosts that decode user-supplied images, correlating process termination events with HEIF file ingestion
Apply file-format fuzzing or static analysis to HEIF inputs received at email gateways and upload endpoints

Monitoring Recommendations

Log image-processing service exits with non-zero status codes and forward to a centralized analytics platform
Alert on abnormal volumes of HEIF or AVIF uploads originating from a single source
Track libheif package versions across the fleet and flag hosts that have not received the 1.22.1 update

How to Mitigate CVE-2026-49271

Immediate Actions Required

Upgrade libheif to version 1.22.1 or later on all systems that decode HEIF or AVIF content
Rebuild and redeploy downstream applications that statically link libheif
Restrict acceptance of HEIF and AVIF files at perimeter gateways until patching is complete

Patch Information

The maintainers fixed the issue in libheif 1.22.1 by hardening the icef offset and size validation against integer overflow. Refer to the GitHub Security Advisory GHSA-r7qj-cg5r-r6vf for the upstream commit and release notes.

Workarounds

Disable the uncompressed HEIF code path in build configurations where the feature is not required
Block HEIF and AVIF file extensions and MIME types at email and web upload boundaries until upgrades land
Sandbox image-decoding processes so that a crash does not impact the parent service

bash

# Verify the installed libheif version on Debian/Ubuntu hosts
dpkg -l | grep libheif

# Verify on RPM-based distributions
rpm -qa | grep libheif

# Build from source against the fixed release
git clone https://github.com/strukturag/libheif.git
cd libheif
git checkout v1.22.1
mkdir build && cd build
cmake --preset=release ..
cmake --build .