CVE-2026-44368 Overview
CVE-2026-44368 is a timing side-channel vulnerability in PyQuorum, a Python cryptographic library used for secret sharing and key management. The flaw resides in the mul_mod function, which performs modular multiplication using a binary expansion loop. The loop's execution time correlates with the Hamming weight of the second operand, leaking information about secret values. An attacker who can measure the latency of secret-sharing operations through a remote service can progressively recover share values and reconstruct the underlying secret. The issue is classified under [CWE-208] (Observable Timing Discrepancy) and is fixed in version 0.2.1.
Critical Impact
Remote attackers measuring operation timing can recover Shamir-style secret shares and reconstruct cryptographic secrets without authentication.
Affected Products
- PyQuorum versions prior to 0.2.1
- Applications embedding PyQuorum for secret sharing
- Remote services exposing PyQuorum secret-sharing operations
Discovery Timeline
- 2026-05-13 - CVE-2026-44368 published to NVD
- 2026-05-13 - Last updated in NVD database
Technical Details for CVE-2026-44368
Vulnerability Analysis
The vulnerability is a classic non-constant-time cryptographic implementation defect. PyQuorum's mul_mod function implements modular multiplication through a square-and-multiply style binary expansion of the second operand. The loop conditionally performs an addition step only when a bit in the operand is set, so the total runtime scales linearly with the number of set bits, the Hamming weight, of that operand.
When the second operand is secret material, such as a Shamir share coefficient, the observable runtime leaks the Hamming weight of that secret. Repeated measurements across many operations allow statistical recovery of individual bits.
Root Cause
The root cause is a data-dependent control flow inside mul_mod. Each iteration of the binary expansion loop branches on a bit of the operand and skips the accumulation step when the bit is zero. This branch-on-secret pattern violates constant-time programming requirements for cryptographic primitives handling private inputs.
Attack Vector
An unauthenticated network attacker invokes the secret-sharing operation against a remote service and records response latencies. By collecting a sufficient number of timing samples for operations involving the same secret share, the attacker recovers the Hamming weight and eventually the full bit pattern of the share. Once enough shares are recovered, the attacker reconstructs the original secret using the underlying secret-sharing scheme.
Verified proof-of-concept code is not published. Refer to the GitHub Security Advisory GHSA-7r92-3jgr-r65q for the maintainer's technical analysis.
Detection Methods for CVE-2026-44368
Indicators of Compromise
- Unusually high volumes of repeated secret-sharing or key-derivation requests from a single source over short time windows.
- Network traffic patterns consistent with timing oracle probing, such as fixed-payload requests with high request rates.
- Application logs showing repeated invocations of PyQuorum share-generation endpoints by unauthenticated clients.
Detection Strategies
- Inventory Python dependencies and flag installations of pyquorum at versions below 0.2.1.
- Instrument services that expose PyQuorum operations to log per-request latency and source IP for offline analysis.
- Apply rate-based anomaly detection to endpoints handling cryptographic operations to surface high-frequency probing.
Monitoring Recommendations
- Monitor egress and ingress request rates on services performing secret sharing for sustained bursts from a single client.
- Track software bill of materials (SBOM) data for the vulnerable pyquorum package version across build pipelines.
- Alert on long-running client sessions that repeatedly invoke identical cryptographic endpoints.
How to Mitigate CVE-2026-44368
Immediate Actions Required
- Upgrade PyQuorum to version 0.2.1 or later in all environments that use the library.
- Audit applications and services for any exposure of PyQuorum operations to untrusted network clients.
- Rotate any cryptographic secrets that were processed by vulnerable PyQuorum versions in network-reachable services.
Patch Information
The maintainer released a fix in PyQuorum 0.2.1 that replaces the timing-variable multiplication routine. See the GitHub Security Advisory GHSA-7r92-3jgr-r65q for patch references and upgrade instructions.
Workarounds
- Place affected services behind authenticated, rate-limited gateways to reduce attacker ability to collect timing samples.
- Add randomized response delays to endpoints that invoke mul_mod until the upgrade is applied, recognizing this only raises attacker cost.
- Restrict access to secret-sharing endpoints to trusted internal networks until the upgrade to 0.2.1 is deployed.
# Configuration example
pip install --upgrade 'pyquorum>=0.2.1'
pip show pyquorum | grep -i version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
