CVE-2026-20911: LibRaw HuffTable::initval Heap Buffer Overflow (CVSS 9.8)

Executive Summary

A critical heap-based buffer overflow vulnerability (CVE-2026-20911) has been identified in LibRaw, a widely-deployed open-source library for reading RAW image formats from digital cameras. The flaw is in the HuffTable::initval function — a component of LibRaw's Huffman decoding pipeline used to initialize lookup tables for compressed RAW image data.

CVSS Score: 9.8 (Critical)

The vulnerability affects two separate LibRaw commits (0b56545 and d20315b), indicating the flaw has persisted across multiple development snapshots. Successful exploitation via a maliciously crafted RAW file could allow an attacker to achieve arbitrary code execution in any process that uses LibRaw to parse images.

Vulnerability Overview

Affected Products

LibRaw is embedded in a wide range of image processing applications including darktable, RawTherapee, digiKam, Photoshop (via Camera Raw plugin), GIMP (via UFRaw/darktable), and numerous scientific and forensic imaging tools.

Technical Analysis

Root Cause

The HuffTable::initval function is part of LibRaw's Huffman decompression implementation, responsible for initializing Huffman lookup tables used to decode compressed RAW image data. The vulnerability arises from insufficient bounds checking during the initialization phase.

When processing a maliciously crafted RAW file, the function can be manipulated — via controlled header values — to write Huffman table entries beyond the bounds of the heap-allocated table buffer. This produces a classic heap buffer overflow that corrupts adjacent heap structures.

Why HuffTable is Dangerous to Overflow

Huffman tables are initialized early in the RAW decoding process and are sized based on values read from the file header. If an attacker can control the number of Huffman codes or the code length distribution declared in the file header without those values being validated against the allocated buffer size, they gain the ability to:

1. Write attacker-controlled data past the end of a heap buffer
2. Corrupt adjacent heap chunk metadata
3. Potentially overwrite function pointers, vtable entries, or other control-flow relevant data stored on the heap

Attack Flow

1. Attacker crafts a RAW file with manipulated Huffman table header declarations
2. Victim (or automated service) passes the file to a LibRaw-linked application
3. LibRaw calls HuffTable::initval to initialize the decompression lookup table
4. The function reads table size parameters from file header without full validation
5. Buffer is allocated based on header values; write operations exceed allocated size
6. Heap corruption occurs — adjacent allocations overwritten
7. Controlled heap corruption may be leveraged for code execution

Impact Assessment

Remediation

Step 1: Check LibRaw Version and Commit

# Check installed LibRaw version
dpkg -l libraw* 2>/dev/null || rpm -q LibRaw 2>/dev/null
 
# On macOS
brew info libraw
 
# Check library version
pkg-config --modversion libraw 2>/dev/null

Step 2: Update to Patched Version

Monitor the LibRaw GitHub repository and apply patches immediately upon release:

# Debian/Ubuntu
sudo apt update && sudo apt install --only-upgrade libraw-dev
 
# RHEL/CentOS/Fedora
sudo dnf update LibRaw
 
# macOS (Homebrew)
brew upgrade libraw
 
# Build from source (when patch is released)
git clone https://github.com/LibRaw/LibRaw.git
cd LibRaw
git pull origin master
./configure && make && sudo make install

Step 3: Update Dependent Applications

After patching LibRaw, check for updates to applications that statically link LibRaw:

# Check which installed packages depend on libraw
# Debian/Ubuntu
apt-cache rdepends libraw23
 
# RHEL/Fedora
dnf repoquery --whatrequires LibRaw

Step 4: Sandboxing Mitigation

Until a patch is applied, run image processing in a sandboxed environment:

# Example: run darktable with firejail sandboxing
firejail --seccomp darktable
 
# Or use bubblewrap for containerized image processing
bwrap --ro-bind /usr /usr --ro-bind /lib /lib --tmpfs /tmp \
  darktable --batch-export /tmp/input.raw /tmp/output.jpg

Detection Indicators

Post-Remediation Checklist

1. Patch LibRaw system-wide as soon as upstream releases the fix
2. Rebuild or update all applications that statically link LibRaw
3. Validate image processing pipelines — ensure untrusted files are sandboxed
4. Enable heap protections (MALLOC_CHECK_=3, ASAN in development) for LibRaw-linked builds
5. Monitor for similar issues — this CVE is one of several heap overflow findings in LibRaw (see CVE-2026-20889, CVE-2026-21413)

References

• NVD — CVE-2026-20911
• LibRaw Official Repository
• Related: CVE-2026-20889 — LibRaw x3f_thumb_loader Heap Buffer Overflow
• Related: CVE-2026-21413 — LibRaw lossless_jpeg_load_raw Heap Buffer Overflow