CVE-2020-7064: PHP EXIF Information Disclosure Flaw

CVE-2020-7064 Overview

CVE-2020-7064 is an out-of-bounds read vulnerability affecting PHP's EXIF data parsing functionality. When processing EXIF metadata using the exif_read_data() function, maliciously crafted data can cause PHP to read one byte of uninitialized memory. This memory safety flaw could potentially lead to information disclosure or application crash, impacting systems that process user-supplied image files containing EXIF metadata.

Critical Impact

Attackers can craft malicious image files with manipulated EXIF data to trigger uninitialized memory reads, potentially leaking sensitive information or causing denial of service conditions on vulnerable PHP installations.

Affected Products

• PHP versions 7.2.x below 7.2.9
• PHP versions 7.3.x below 7.3.16
• PHP versions 7.4.x below 7.4.4
• Debian Linux 8.0, 9.0, 10.0
• Ubuntu Linux 12.04 ESM, 14.04 ESM, 16.04 LTS, 18.04 LTS, 19.10, 20.04 LTS
• openSUSE Leap 15.1
• Tenable.sc (versions prior to fix)

Discovery Timeline

• 2020-04-01 - CVE-2020-7064 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-7064

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-Bounds Read), a memory safety issue where the application reads data from a memory location outside the intended buffer boundaries. The flaw resides in PHP's EXIF parsing module, specifically within the exif_read_data() function that processes Exchangeable Image File Format metadata embedded in image files such as JPEGs.

When parsing specially crafted EXIF data, the function fails to properly validate data boundaries before performing read operations. This results in PHP reading one byte of uninitialized memory, which could contain sensitive information from previous operations or cause the application to crash if it accesses invalid memory regions.

Root Cause

The root cause lies in improper bounds checking within PHP's EXIF parsing implementation. The exif_read_data() function processes EXIF tags and data structures from image files without adequately validating the lengths and offsets specified in the EXIF header. When malformed EXIF data specifies incorrect boundary values, the parser continues reading beyond the allocated buffer, accessing uninitialized memory.

This type of vulnerability is common in parsers handling complex binary formats where multiple nested data structures contain their own length and offset fields that must be cross-validated against the overall data size.

Attack Vector

The attack vector requires user interaction—an attacker must convince a victim to process a malicious image file through a PHP application. The exploitation scenario involves:

1. Malicious Image Creation: The attacker crafts an image file (typically JPEG or TIFF) with manipulated EXIF metadata containing invalid boundary specifications
2. Delivery: The malicious image is uploaded to a web application or delivered through other means where PHP's exif_read_data() function will process it
3. Trigger: When the vulnerable PHP application processes the image's EXIF data, the out-of-bounds read occurs
4. Impact: The attacker may obtain one byte of leaked memory contents (information disclosure) or cause the PHP process to crash (denial of service)

The vulnerability is exploitable over the network against web applications that process user-uploaded images, though the limited one-byte read makes significant data exfiltration challenging.

Detection Methods for CVE-2020-7064

Indicators of Compromise

• Monitor for PHP process crashes or segmentation faults occurring during image processing operations
• Watch for unusual patterns of malformed image file uploads targeting EXIF parsing functionality
• Review application logs for errors related to exif_read_data() function calls
• Detect repeated uploads of image files with corrupted or oversized EXIF headers

Detection Strategies

• Implement file integrity monitoring on PHP application directories to detect unauthorized modifications
• Deploy web application firewalls (WAF) with rules to inspect uploaded image files for malformed EXIF data
• Use runtime application self-protection (RASP) to detect anomalous memory access patterns during PHP execution
• Enable PHP error logging and monitor for EXIF-related warnings and fatal errors

Monitoring Recommendations

• Configure centralized logging to aggregate PHP error logs across all web servers
• Set up alerting for elevated rates of image processing failures or PHP crashes
• Monitor memory utilization patterns that may indicate exploitation attempts
• Implement SentinelOne's behavioral AI to detect anomalous process behavior associated with memory corruption exploitation

How to Mitigate CVE-2020-7064

Immediate Actions Required

• Upgrade PHP immediately to version 7.2.9 or later for 7.2.x branch, 7.3.16 or later for 7.3.x branch, or 7.4.4 or later for 7.4.x branch
• Apply vendor-supplied security patches from Debian, Ubuntu, openSUSE, or other distribution maintainers
• Audit applications to identify all locations where exif_read_data() is called
• Consider implementing input validation to pre-screen image files before EXIF processing

Patch Information

Security patches addressing this vulnerability have been released by PHP and major Linux distributions. The official PHP bug report PHP Bug Report #79282 contains details about the fix. Distribution-specific patches are available through:

• Debian Security Announcement DSA-4717 and DSA-4719
• Ubuntu Security Notice #4330-1 and #4330-2
• openSUSE Security Announcement
• Tenable Security Notice TNS-2021-14 for Tenable.sc users

Workarounds

• Disable the PHP EXIF extension if exif_read_data() functionality is not required by your applications
• Implement application-level validation to reject image files with suspicious EXIF headers before processing
• Use alternative EXIF parsing libraries that are not affected by this vulnerability
• Isolate image processing in sandboxed environments to limit the impact of potential exploitation

# Disable EXIF extension in PHP (if not needed)
# Edit php.ini and comment out or remove:
# extension=exif

# Verify EXIF extension status
php -m | grep -i exif

# Restart web server after configuration changes
sudo systemctl restart apache2  # For Apache
sudo systemctl restart php-fpm  # For PHP-FPM