arXiv subjects

Sergey Bratus

Publications and source records attributed to Sergey Bratus.

4 recordsLinked to original sources

arXiv2026

Trouble at the top: can Python extend the chains of trust in infrastructure firmware?

Compiled Python bytecode (PYC) has become an essential part of network switches, routers, and other network infrastructure devices. Our analysis shows that its integrity is implicitly trusted in multiple designs that make use of Python code at the top of the operational software, such as the management and control pane of enterprise network switches. At the same time, the integrity of PYC files is not covered under the traditional chain-of-trust models, due to complex interactions with the CPython loader, byte compiler, and other Python runtime components. We explore the risks inherent in including PYC and Python runtimes in the de facto trusted code basis of commercial enterprise equipment and offer a comprehensive framework for understanding emergent behaviors in these designs.

cs.CR↗

arXiv2026

TLF: Rapid Characterization of RF Transceiver Parameters in Embedded Systems via Bus-Level Interception

We present TLF (Transceiver Lifter Framework), a tool for recovering RF transceiver configuration and runtime behavior from bus-level traces captured between a microcontroller and its transceiver IC. A stateful protocol decoder, built against the transceiver's register and data interface, reconstructs operating RF parameters and behavior from intercepted register writes and FIFO transfers. For bus-attached transceivers whose hardware-cryptography keys are loaded through the intercepted host interface, key material is also recoverable. Where the firmware drives frequency hopping -- either through a hardware-assisted engine or a custom schedule -- the decoder extracts the channel table, hop sequence, and timing. We evaluate the approach on two targets from different Semtech families: an SX1233-based UAV C2 modem employing firmware-level FHSS with per-packet sync word rotation, and an SX1276-based Meshtastic node exercising the LoRa register overlay. From a single bus capture, processed in seconds, TLF recovers the complete register-exposed RF configuration (modulation, band plan, phase behavior) without prior knowledge of the target firmware -- sufficient to configure a matched receiver or develop targeted countermeasures. Above the chip layer, a pluggable protocol decoder interprets recovered FIFO payloads as application PDUs, demonstrated end-to-end on Meshtastic. Firmware-level cryptographic state remains, as expected, opaque. The approach requires physical access or emulation of the target hardware, and its recovery depth is bounded by the transceiver's register interface: parameters implemented entirely in firmware (custom FEC, whitening, encryption) are observable only as opaque FIFO payloads.

cs.CR↗

arXiv2026

The Hidden Life of Public Safety Communications Signals: A Comparative Security Analysis of TETRA, TETRAPOL, and P25

Public-safety agencies and critical infrastructure operators rely on trunked land-mobile radio (LMR) systems, based on P25, TETRA, and TETRAPOL. These systems are expected to protect not just the content of a communication but the fact of it. Yet LMR standards leave a stark gap between confidentiality of \emph{content} and of \emph{communication}: underneath an encrypted traffic plane, their signaling plane is almost entirely in the clear. We probe the depth and impact of adversarial inference from this exposed signaling. Prior security analyses of these systems have concentrated on the content plane---recovering encryption keys or capturing accidental cleartext. We show that comparably sensitive information can be \emph{inferred from passively observed signaling even if the content encryption were perfect}. In particular, we show that across the trunked LMR standards, a passive, receive-only software-defined radio (SDR) observer can recover operationally sensitive network topology and geography details, unit presence, mobility across cells and groups, organizational structure, as well as operational security details such as special key domains and key-epoch rotation. This signaling-plane inference reaches far beyond the observer's direct area of reception, turning \emph{local} sniffing into \emph{nationwide} network mapping capabilities that degrade or defeat LMR standards' identity obfuscation through timing and association. In the case of TETRAPOL, we demonstrate how inference and tracking of such signaling metadata and a standards-level confidentiality failure in emergency call handling enable unencrypted voice extraction. Finally, we discuss potential countermeasures and mitigations, including specific recommendations for protecting inter-cell, base station and subscriber identities.

cs.CR↗

arXiv2026

WAFFLED: Exploiting Parsing Discrepancies to Bypass Web Application Firewalls

Web Application Firewalls (WAFs) have been introduced as essential and popular security gates that inspect incoming HTTP traffic to filter out malicious requests and provide defenses against a diverse array of web-based threats. Evading WAFs can compromise these defenses, potentially harming Internet users. In recent years, parsing discrepancies have plagued many entities in the communication path; however, their potential impact on WAF evasion and request smuggling remains largely unexplored. In this work, we present an innovative approach to bypassing WAFs by uncovering and exploiting parsing discrepancies through advanced fuzzing techniques. By targeting non-malicious components such as headers and segments of the body and using widely used content-types such as application/json, multipart/form-data, and application/xml, we identified and confirmed 1207 bypasses across 5 well-known WAFs, AWS, Azure, Cloud Armor, Cloudflare, and ModSecurity. To validate our findings, we conducted a study in the wild, revealing that more than 90% of websites accepted both application/x-www-form-urlencoded and multipart/form-data interchangeably, highlighting a significant vulnerability and the broad applicability of our bypass techniques. We have reported these vulnerabilities to the affected parties and received acknowledgments from all, as well as bug bounty rewards from some vendors. Further, to mitigate these vulnerabilities, we introduce HTTP-Normalizer, a robust proxy tool designed to rigorously validate HTTP requests against current RFC standards. Our results demonstrate its effectiveness in normalizing or blocking all bypass attempts presented in this work.

cs.CR↗