Behind the Curtain of the July 2025 SharePoint Zero Day: My Unfiltered Take

Before last week, I would’ve put betting money on July being a quiet month—until the SharePoint zero-day (CVE-2025-53770) explosion hit. Sitting at my desk, half-writing a script and half-daydreaming about DEFCON, I watched as Slack and Twitter lit up with panicked questions. What was most unsettling? The sense that we were watching history repeat—again. Here’s my boots-on-the-ground look at what it’s really like riding the first wave of a cyberstorm, plus a few wild cards you won’t read in your average advisory.

Microsoft SharePoint Falls Again: The Anatomy of CVE-2025-53770

Let’s get right to it—July 2025 delivered another blow to Microsoft SharePoint’s reputation for security. The CVE-2025-53770 vulnerability emerged as a classic example of how a single flaw can ripple across the globe, leaving more than 75 organizations, including major corporations and government agencies, compromised. I remember reading the initial advisory and thinking, “Here we go again.” The SharePoint zero day was officially announced by Microsoft on July 19, 2025, but the exploit was already active in the wild before that.

What makes this vulnerability so alarming? For starters, it scored a staggering 9.8 on the CVSS scale—just a hair away from the maximum. That’s not just a red flag; it’s a blaring siren. This flaw enables unauthenticated remote code execution on on-premises SharePoint servers. In plain English, attackers don’t even need a password. All it takes is a carefully crafted HTTP request, and they’re in.

Here’s a quick breakdown of how the attack unfolded:

• The exploit chain starts with CVE-2025-49706 and CVE-2025-49704, both previously known Microsoft SharePoint vulnerabilities.

• Attackers use these to upload a malicious web shell—often named spinstall0.aspx—to the server.

• This web shell then extracts cryptographic secrets (like ValidationKey and DecryptionKey) from SharePoint, enabling attackers to forge authentication tokens and maintain persistent access.

As research shows, this “ToolShell exploit” chain is particularly dangerous because even if you remove the initial web shell, the attackers can still get back in using forged credentials. The initial wild discovery of this exploit was made by the iSecurity team on July 18th. In their words:

"The exploit was originally found in the wild by the team at iSecurity on July eighteenth."

At the time of Microsoft’s disclosure, there was no patch available—just urgent guidance from both Microsoft and CISA. That left IT teams scrambling, especially since the vulnerability only affects on-premise SharePoint instances, not Microsoft 365 cloud deployments. Still, the impact was immediate and widespread.

The CVE-2025-53770 vulnerability is a stark reminder that SharePoint zero day threats are not just theoretical—they’re happening now, and the consequences are real.

Dissecting ToolShell: How Attackers Walked Right In

Let’s get into the gritty details of the ToolShell exploit chain—because if you want to understand modern SharePoint attack stages, you need to see how attackers stitched together CVE-2025-49706 and CVE-2025-49704. These vulnerabilities, now infamous in the security community, form the backbone of the ToolShell exploit. The first, CVE-2025-49706, allowed attackers to bypass authentication using a manipulated header. Microsoft patched it, but as research shows, the patch didn’t hold up for long. The second, CVE-2025-49704, took things further, enabling remote code execution (RCE) in a way that’s both elegant and terrifying.

What really sets ToolShell apart is how it abuses SharePoint’s ViewState feature. For those unfamiliar, ViewState is a mechanism in ASP.NET that stores page and control values between requests. Normally, it’s a helpful tool for web developers. But here’s where things get dicey: ToolShell leverages a deserialization flaw in ViewState, letting attackers inject payloads that the server treats as legitimate. This isn’t just a technicality—it’s a fundamental breakdown in trust.

The real magic (or mayhem, depending on your perspective) happens when attackers extract cryptographic secrets straight from SharePoint’s memory. We’re talking about the ValidationKey and DecryptionKey. With these, attackers can forge valid tokens and sign their own ViewState payloads. As one researcher put it:

"Once this cryptographic material is leaked, the attacker can craft fully valid signed view state payloads using a tool called Wysoserial."

This is where the Wysoserial tool comes into play. It allows attackers to create spoofed ViewState payloads that are indistinguishable from legitimate traffic. These payloads can embed any command the attacker wants, and SharePoint will execute them without question. Even if you applied the initial patch, ToolShell’s exploit chain still works—demonstrating just how advanced and persistent these attack techniques have become.

Once inside, attackers often deploy the spinstall0.aspx web shell. This gives them a stealthy, persistent presence on the server. The attack chain mirrors weaknesses exploited back in 2021, but now it’s automated, persistent, and requires zero authentication. In short, ToolShell is a new generation exploit chain—one that combines multiple vulnerabilities, advanced evasion, and cryptographic secrets extraction to maintain full control.

Mitigation Scramble: Patching in the Eye of a Storm

When Microsoft disclosed the SharePoint zero day (CVE-2025-53770) on July 19th, the cybersecurity world braced for impact. This wasn’t just another vulnerability—this was a remote code execution flaw, actively exploited, and targeting on-premises Microsoft SharePoint servers. If you’re running SharePoint Online through Microsoft 365, you can breathe a little easier (for now), but on-prem admins had no such luxury. The exploit chain, dubbed “tool shell,” leveraged weaknesses in ViewState handling to grant attackers unauthenticated access and full persistence—no credentials required.

The response from Microsoft was swift, but the reality on the ground was anything but calm. At first, there was no patch. As I watched the news break, it was clear: defenders were in a race against time.

“At first report, Microsoft did not have a patch available for the tool shell RCE. Within the day, they announced mitigations and protection guidance.”

That same day, CISA added the CVE to itsKnown Exploited Vulnerabilities (KEV) list, signaling the highest level of urgency. In my experience, when a zero day lands on the KEV list this quickly, you know attackers are already inside some networks.

Here’s the hard truth: even with rapid CISA guidance updates and Microsoft’s best efforts, real-world mitigation often lags behind attacker progress. Research shows that proactive detection is critical in the zero-day window. Patches are essential, but sometimes they arrive after the damage is done. That’s why my unofficial advice is simple—don’t sleep on detection. While you’re racing to apply updates, attackers may already be deploying web shells or extracting cryptographic secrets.

• Monitor for new shells: Watch for unexpected files like spinstall0.aspx appearing on your SharePoint servers.

• Examine ViewState anomalies: Unusual ViewState payloads or validation errors can be early warning signs of exploitation.

• Think beyond the official bulletins: Attackers often innovate faster than vendors can publish guidance. Don’t rely solely on patch notes—invest in behavioral monitoring and anomaly detection.

The mitigation and patch timeline was a blur: initial advisory on July 19, mitigations within hours, and a security update shortly after. Still, as the dust settled, it was clear that only on-premises SharePoint servers were confirmed at risk. Microsoft 365’s online SharePoint remained unaffected, but as always, caution is warranted—attackers are nothing if not persistent.

Where the Money Goes: Cyber Budgets, Policy Pivots, and Unintended Chaos

Let’s pull back the curtain on a topic that’s been quietly reshaping our national cybersecurity posture: the Department of Defense cyber budget. In July 2025, as the world was still reeling from the fallout of the SharePoint zero day, the U.S. government passed a bill allocating a staggering $1 billion to the DoD for cyber offensive operations over the next four years. On the surface, this sounds like a decisive move—finally, big money to counter advanced threats, right? But the reality is more complicated, and, frankly, a bit unsettling.

Here’s the catch: while the offensive side gets a cash injection, the defensive side is being gutted. Federal cyber defense budgets are being slashed, and CISA—America’s front line for cyber defense—is facing layoffs and program reductions. As one observer put it,

"This comes into direct contrast with the aggressive slashing of budget for US defensive cyber operations, including the gutting of CISA, budget reductions, and employee layoffs."

This is where the real chaos begins. The cyber policy changes impact not just the agencies involved, but the entire ecosystem of public and private sector defense. Senators on both sides of the aisle have started warning about the potential blowback from this offense-heavy approach. If you ask me, it’s like rewiring the alarm system while the building is still on fire. We’re shifting resources to kick down doors overseas, but leaving our own windows wide open at home.

Research shows that budget swings like these can create exploitable gaps in our national cybersecurity posture. When defense is weakened—especially at a time when zero-day vulnerabilities like CVE-2025-53770 are actively being exploited—attackers notice. The recent SharePoint exploit chain, dubbed "ToolShell," is a perfect example. Attackers leveraged a complex chain of vulnerabilities to gain persistent, unauthenticated access to critical infrastructure. The rapid response from Microsoft and the CISA guidance update were essential, but what happens if the teams responsible for detection and mitigation are underfunded or understaffed?

The cybersecurity developments of July 2025 highlight a dangerous imbalance. Policy pivots that favor offense over defense can backfire, potentially inviting more attacks or even retaliation. In my view, the Department of Defense cyber budget boost should have been matched with equal investment in defense. Otherwise, we risk creating the very chaos we’re trying to prevent.

Ransoms, Rebrands, and the Resilience of Attackers: My Take on World Leaks and the Dell Breach

If you’ve been following the latest cybersecurity developments in July 2025, you’ve probably heard the name World Leaks ransomware group making headlines. Not long ago, I covered the supposed shutdown of Hunters International. But as is often the case in cybercrime, “shutdown” didn’t mean the end—it meant a rebrand. The group resurfaced as World Leaks in late 2024, shifting its focus from traditional ransomware deployment to pure extortion and data theft. It’s a move that says a lot about how these threat actors adapt and evolve.

World Leaks has actually been active since January 2025 and has hit forty-nine organizations. That’s not just a number—it’s a sign of how quickly a rebranded group can regain momentum. The most recent headline-grabber? The Dell data breach. Attackers didn’t just go after customer data or core infrastructure; they targeted Dell’s product demonstration platform. According to Dell, this environment is intentionally isolated from customer and partner systems, and not used in the provision of services to customers. Still, the breach happened, and data leaks persisted.

"World Leaks has actually been active since January twenty twenty five and has hit forty nine organizations."

What’s wild about this scenario is how creative the attacks have become. Instead of encrypting files and holding them hostage, World Leaks is now leveraging stolen data for extortion, threatening to leak sensitive information unless demands are met. This “extortion without encryption” model is becoming the new face of ransomware deployment. It’s faster, it’s harder to defend against, and it often flies under the radar until it’s too late.

Research shows that large-scale data breaches are increasingly targeting non-traditional platforms—think demo environments, development sandboxes, or proof-of-concept systems. These aren’t the obvious targets, but they often hold valuable intellectual property or internal documentation. The Dell incident is a perfect example: attackers flaunted their access to a platform many would consider low-risk, yet the impact was significant enough for World Leaks to add Dell to their growing list of victims.

This isn’t just about one group or one breach. The World Leaks ransomware group is demonstrating a broader trend: rapid rebranding, creative targeting, and an ability to stay one step ahead. As we watch these cybersecurity developments in July 2025 unfold, it’s clear that the resilience of attackers is matched only by their willingness to rewrite the rules of cyber extortion.

Reflecting Forward: DEFCON, Sticker Swaps, and Why Cybersecurity Is Personal

As July 2025 draws to a close, I find myself thinking about the relentless pace of cybersecurity developments. Just last year, the big headlines were all about CrowdStrike. This summer, we’re caught up in the whirlwind of the SharePoint zero day—an incident that’s forced every security team I know to rethink their strategies, patch cycles, and even their sense of what’s possible. The industry never sleeps. There’s always a new remote code execution exploit, a new threat actor, a new lesson to learn. And yet, amid all this chaos, there’s a rhythm to it—an annual cycle that brings us back together, whether it’s in the trenches of incident response or the hallways of DEFCON.

DEFCON, for me, is more than just a conference. It’s a checkpoint for our community—a place where the formalities drop away and real, unfiltered knowledge sharing happens. I look forward to the sticker swaps, the spontaneous hallway meetups, and the late-night war stories about living on the bleeding edge. These traditions might seem trivial to outsiders, but they’re the glue that holds our community together. Every sticker, every handshake, every shared laugh over a failed exploit attempt is a reminder that behind every headline—whether it’s a SharePoint zero day or a ransomware campaign—there are real people learning, adapting, and supporting each other.

This year, as I pack up a fresh batch of ThreatWire stickers for DEFCON, I’m reminded that cybersecurity isn’t just about technology. It’s deeply personal. Every incident leaves its mark—lessons learned, regrets over what we missed, small victories, and sometimes just a bit of luck. Research shows that personal connection and continual learning are what make our industry resilient, no matter the threat. The hacker ethos—curiosity, community, and cautious optimism—drives cyber defense as much as the latest patch or detection tool.

So, as we move forward from the SharePoint chaos of July 2025, I encourage everyone to stay curious, stay connected, and never underestimate the power of a hallway conversation or a sticker swap. If you see me at DEFCON, please come up and say hi. In the meantime, if you want to find me online, you can find me everywhere at ending with Ally.

"If you see me at Defcon, please come up and say hi. In the meantime, if you want to find me online, you can find me everywhere at ending with Ally."