Glm 5 3 And The Spread Of Advanced Cyber Capabilities

GLM-5.3 and the spread of advanced cyber capabilities \ Anthropic Frontier Red Team Policy GLM-5.3 and the spread of advanced cyber capabilities Sep 29, 2026

Andrew Fasano, Marius Fleischer Cole McFaul, Robert Xiao, Tripp Gallagher Five months ago, we announced Claude Mythos Preview, the first AI model that could autonomously build sophisticated, end-to-end cyber exploits. The rapid rate of improvement in AI suggested to us that this ability would eventually proliferate to many other models, making it much easier for malicious cyber actors to launch highly impactful cyberattacks. In light of these considerations, we chose to release Claude Mythos Preview in a limited way, through Project Glasswing—which enabled trusted cyber defenders to find more than 10,000 vulnerabilities in critical software, giving them a head start before malicious actors had access to similarly capable models. But those models have now arrived. In this post, we share our analysis of GLM-5.3, the latest AI model developed by Zhipu AI (known outside of China as Z.ai). Like Claude Mythos Preview, GLM-5.3 has strong capabilities for autonomously building end-to-end cyber exploits. But GLM-5.3 is unlike other frontier models in that it has been released without meaningful safeguards to limit misuse. We find that attackers can bypass GLM-5.3’s safeguards between 64% and 100% of the time with simple techniques in our simulated tests. In contrast, these attacks did not succeed against safeguarded Claude models in our testing. We assess that GLM-5.3’s lax safeguards significantly increase the cyber capabilities available to malicious actors. At the same time, these capabilities can also benefit defenders working to secure their systems. On Sept. 17, NIST’s Center for AI Standards and Innovation (CAISI) published its own assessment of GLM-5.3’s cyber capabilities. CAISI found that GLM-5.3 is “the most cyber-capable open-weight model released to date” and that it lags the US frontier by about four months on an aggregate of CAISI’s cyber benchmarks. Our capability findings broadly match CAISI’s. In CAISI’s comparison, US models were tested with cyber safeguards disabled when applicable, and the US frontier includes models released only to vetted users. Attackers can’t readily access those versions of US models, but anyone can download GLM-5.3. This post adds our analysis of how easily GLM-5.3’s safeguards can be bypassed or removed. Figure 1. Summary of findings. Top: The increase in exploitation capability between Claude Opus 4.6 and Claude Mythos Preview mirrors the jump in capabilities between GLM-5.2 and GLM-5.3. Claude models are released with cyber safeguards, and versions with reduced safeguards are limited to vetted users. Anyone can download and use GLM-5.3. Bottom: The limited safeguards in GLM-5.3 can be bypassed with standard techniques that did not work against, or do not apply to, Claude models in our testing. GLM-5.3 can develop working exploits end to end To understand how GLM-5.3 could enable cyber threat actors to find and exploit real software vulnerabilities, we ran evaluations using automated benchmarks and human-in-the-loop workflows. For both approaches, we ran the tested models in isolated and sandboxed environments so they can only attack offline targets that we have set up for the purposes of these evaluations. We focus primarily on exploit development capability, as this is where Claude Mythos Preview demonstrated a notable jump versus previous Claude models. First, we ran the model on ExploitBench , which measures how well AI models can exploit known vulnerabilities in the V8 engine used by Google Chrome. Here we focus on the models’ ability to develop end-to-end exploits successfully, as this is the most relevant capability for attackers, and where we see significant changes between models. We find that GLM-5.3 develops end-to-end exploits in 50 of 410 attempts. Claude Mythos Preview did so at a similar rate—in 56 of 410 attempts. In our internal Binary Exploitation benchmark, 1 we test whether models can find and exploit vulnerabilities in popular open source projects that participate in Google’s OSS-Fuzz project. Here, full credit is awarded for a full control-flow hijack. We evaluate several models on 100 tasks from the benchmark (selected at random), and find that GLM-5.3 develops full control flow hijacks in 4% of the trials; Claude Mythos Preview did so in 6%. Although GLM-5.3 performs below Claude Mythos Preview here, a meaningful threshold has clearly been crossed: earlier models, like Claude Opus 4.6 and GLM-5.2, do not succeed in any of them. Figure 2. Exploitation capability versus output-token budget. Each line shows the share of a model’s attempts that reached the benchmark’s top outcome versus the output tokens used. Both figures show performance of two Claude models run with safeguards disabled (Opus 4.6, Mythos Preview), two GLM models (5.2 and 5.3), and results from the latest open-weight models released by Moonshot AI (Kimi K3) and DeepSeek (V4.1-Flash). Next, we evaluated how GLM-5.3 performs on open-ended offensive cyber tasks in the hands of human experts (mirroring our testing with Claude Mythos Preview earlier this year). Here, we select targets in which the human experts are unaware of existing vulnerabilities, then ask them to use the model to identify and exploit novel flaws. These experiments tested what the experts could do in a short time-frame: they typically ran for a day or less, with less than an hour of human focus in total. Figure 3. A redacted screenshot of an exploit page generated by GLM-5.3 during researcher-driven testing, shown stealing a user’s SSH private key via a malicious website. The exploit chains together multiple 0-day vulnerabilities the model discovered in a component of a popular web browser, reading a sensitive file off the user’s computer. In the first of these sessions, a researcher used GLM-5.3 on a sandboxed machine with a local Linux build of a popular web browser. Over the course of a day (and with limited human attention), GLM-5.3 found several previously unknown vulnerabilities in the browser’s JavaScript engine, and chained them together into a working exploit: a webpage that, when visited, reads arbitrary files from the visitor’s computer (shown in Figure 3). This exploit targets the Linux build of the browser, since that was the only environment made available to the model. However, we believe these vulnerabilities could...