CVE-2026-31961 Overview
CVE-2026-31961 is an unbounded memory allocation vulnerability affecting Quill, a tool that provides simple Mac binary signing and notarization from any platform. The vulnerability exists in Quill versions prior to v0.7.1 and can be exploited when the application parses specially crafted Mach-O binaries containing malicious size values in code signing structures.
Critical Impact
An attacker can craft a minimal (~4KB) malicious Mach-O binary that causes Quill to attempt excessive memory allocation, leading to memory exhaustion and denial of service in CI/CD pipelines, shared signing services, or any workflow processing externally-submitted binaries.
Affected Products
- Quill CLI versions prior to 0.7.1
- Quill Go library versions prior to 0.7.1
- Systems using Quill for automated Mac binary signing and notarization
Discovery Timeline
- 2026-03-11 - CVE CVE-2026-31961 published to NVD
- 2026-03-12 - Last updated in NVD database
Technical Details for CVE-2026-31961
Vulnerability Analysis
This vulnerability is classified as CWE-770 (Allocation of Resources Without Limits or Throttling). The flaw resides in Quill's Mach-O binary parsing logic, which reads size and count fields from code signing structures without validating that these values are reasonable or consistent with the actual file size.
When Quill processes a Mach-O binary, it parses the LC_CODE_SIGNATURE load command and embedded code signing structures including SuperBlob and BlobIndex. The parser reads several critical fields and uses them directly for memory allocation without bounds checking. Affected fields include DataSize, DataOffset, and Size from the load command, Count from the SuperBlob header, and Length from individual blob headers.
Both the Quill command-line interface and the Go library are affected when used to parse untrusted Mach-O files. The vulnerability is particularly concerning in automated environments where external binaries are accepted for signing without prior validation.
Root Cause
The root cause is improper input validation in the Mach-O parsing routines. Quill trusts attacker-controlled values from the binary file structure and uses them directly to allocate memory buffers. The application fails to validate that size fields are consistent with the actual file size before performing allocations, allowing an attacker to specify arbitrarily large values that exhaust available memory.
Attack Vector
Exploitation requires that Quill processes an attacker-supplied Mach-O binary. This is most likely to occur in environments such as CI/CD pipelines, shared signing services, or any workflow where externally-submitted binaries are accepted for signing.
An attacker crafts a minimal malicious Mach-O binary (approximately 4KB in size) with extremely large values in the affected size and count fields. When Quill attempts to parse this binary, it reads these malicious values and attempts to allocate excessive amounts of memory, causing memory exhaustion and crashing the host process.
The attack requires local access and low privileges to execute. While there is no impact on confidentiality or integrity, the availability impact is high as it can completely crash the signing service.
Detection Methods for CVE-2026-31961
Indicators of Compromise
- Unexpected memory spikes in processes running Quill binary signing operations
- Quill process crashes with out-of-memory errors in CI/CD pipeline logs
- Mach-O binaries submitted for signing with abnormally large values in LC_CODE_SIGNATURE structures
- Process termination events correlated with binary signing operations
Detection Strategies
- Monitor memory consumption of Quill processes and alert on unusual allocation patterns
- Implement pre-validation of Mach-O binaries before passing them to Quill for signing
- Add logging to capture the size fields from LC_CODE_SIGNATURE load commands and SuperBlob structures
- Review CI/CD pipeline logs for repeated Quill process failures or restarts
Monitoring Recommendations
- Set up resource limits (memory cgroups) for processes handling untrusted binary signing
- Implement process monitoring to detect and alert on abnormal memory usage by Quill
- Log all binary submissions to signing services for forensic analysis
- Monitor for unusual patterns of failed signing operations that may indicate exploitation attempts
How to Mitigate CVE-2026-31961
Immediate Actions Required
- Upgrade Quill to version 0.7.1 or later immediately
- Audit CI/CD pipelines and signing services to identify all instances of vulnerable Quill versions
- Implement input validation on submitted binaries before processing with Quill
- Apply resource limits to containers or processes running Quill to contain potential denial of service
Patch Information
The vulnerability is fixed in Quill version 0.7.1. Organizations should upgrade all Quill CLI installations and update any Go projects using the Quill library to the patched version. For detailed patch information, refer to the GitHub Security Advisory.
Workarounds
- Implement memory limits using cgroups or container resource constraints to prevent system-wide impact
- Add pre-parsing validation of Mach-O binaries to check that size fields are reasonable relative to file size
- Isolate Quill processing in sandboxed environments to contain potential crashes
- Restrict binary submissions to trusted sources only until the patch can be applied
# Example: Apply memory limits to Quill process using systemd
# Create systemd override to limit memory allocation
sudo systemctl edit quill-signing.service
# Add the following configuration:
# [Service]
# MemoryMax=512M
# MemorySwapMax=0
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
