Researchers uncovered a zero-day vulnerability in the 7-Zip archiving utility that was actively exploited in the context of Russia’s ongoing military actions in Ukraine. The flaw let a Russian cybercrime group override Windows protections designed to limit the execution of files downloaded from the Internet. This defense, commonly known as the Mark of the Web (MotW), attaches a Zone.Identifier on files obtained from the Internet or a networked share. The Zone Identifier is a form of NTFS Alternate Data Stream that flags the file with a ZoneID value, subjecting it to extra scrutiny by Windows Defender SmartScreen and imposing restrictions on when or how the file can run. The compromise arose from a specific weakness in how 7-Zip propagated these protections through nested archives, enabling attackers to bypass the MotW safeguards and execute malicious content on victims’ machines. The vulnerability, designated CVE-2025-0411, was addressed with the release of 7-Zip version 24.09 in late November.
What happened and how the attack worked
The MotW mechanism and Windows defenses
To understand the attack, it helps to grasp how MotW and its protective posture operate in Windows environments. When a file is downloaded from the Internet, Windows can automatically tag it with a Zone.Identifier data stream. This tag indicates the origin of the file and how it should be treated by the system. The presence of MotW typically triggers heightened scrutiny by security tools such as Windows Defender SmartScreen, potentially delaying or blocking execution and prompting the user to confirm whether they want to run the file. This model is designed to reduce the likelihood that downloaded executables or scripts will run automatically, especially when the source is uncertain or external.
The double-archive technique and the bypass
The 7-Zip vulnerability revolved around double-encapsulated archives. In practice, an attacker would place an executable file inside one archive, and then place that archive inside another outer archive that is intended to be downloaded and opened by a target user. The key weakness was that the MotW tag would be applied to the outer archive, but not reliably propagated to the contents of the inner archive. As a result, when users opened the outer archive, the inner content could be executed without triggering the MotW-based protections that would normally apply to downloaded content. This gap allowed the attacker’s payload—an executable or a script—to bypass Windows’ initial defense layer and run on the victim’s machine.
How the zero-day was exploited in practice
In this campaign, threat actors embedded an executable file within an inner archive and then enveloped that archive in a second, outer archive that carried the MotW tag. The outer layer’s MotW designation did not automatically flow into the inner layer, thereby sidestepping the multi-layer protection that would ordinarily impede execution. The exploitation relied on the user extracting the outer archive and then launching the inner payload, with the security posture effectively bypassed or weakened by the incomplete propagation of MotW protections across nested archives.
Obfuscation through homoglyphs
To increase the likelihood that targets would engage with the payload, attackers used homograph-like characters—a technique known as homoglyphs. These characters mimic familiar ASCII characters but belong to different Unicode symbols. For example, a Cyrillic character that visually resembles the Latin letter C could be used to disguise the file extension or the name of a file, making the executable appear as a harmless document or document-like attachment. This disguise helps the malicious payload blend in with legitimate documents, raising the chance that recipients will open or execute the file under the impression that it is a benign attachment.
Targeting tactics and the use of compromised accounts
The operators behind this zero-day attack leveraged compromised credentials and accounts to lend legitimacy to their delivery. They distributed double-archived files via email attachments that appeared to originate from real, trustworthy sources. In practice, the attackers used genuine, compromised accounts tied to Ukrainian government entities to further their phishing campaigns. The objective was to attach the double-archived payload to emails that would seem credible to recipients, thus increasing the probability that the target would open the archive and execute the malicious file. This approach underscored a broader trend in contemporary cyber operations that combine technical exploitation with social engineering to maximize impact.
The institutions that appeared in the targeting list
Researchers identified a set of agencies and organizations that were among those observed as potential targets or perceived conduits through which the campaign operated. The list included government and public-interest bodies such as the State Executive Service of Ukraine, the Ministry of Justice, a major vehicle manufacturing plant, and several state and municipal entities involved in public administration, transportation, consumer electronics manufacturing, and essential services. The presence of these targets underscored a focus on critical infrastructure and public sector entities, consistent with a broader pattern of tension-driven cyber activity that seeks to disrupt governance, public services, and civilian life during periods of geopolitical conflict. The entities highlighted in analyses were representative of a broader spectrum of organizations that contemporary threat actors monitor for possible compromise and leverage in campaigns.
Timeline, discovery, and remediation
Discovery and attribution
The vulnerability was identified by a prominent security firm that tracks malware, espionage, botnet activity, and related threats. The researchers documented that the root cause lay in how 7-Zip propagated MotW protections to the contents of archives that were nested within other archives. The finding emphasized that versions prior to the fixed release did not reliably ensure MotW coverage for double-encapsulated content, leaving Windows users exposed to attacks that leveraged this gap. The security firm attributed the flaw to a propagation shortfall in the 7-Zip handling of nested archives and explained how this gap enabled attackers to craft archives containing malicious scripts or executables that would not receive MotW protections, thereby allowing execution in Windows environments prematurely or without adequate defensive triggers.
The fix and version information
The vendor released a fix in version 24.09, which rolled out in late November. The update corrected the propagation of MotW protections into the content inside double-encapsulated archives. By ensuring that the MotW designation was consistently applied to nested components, the patched version raises the bar for attackers attempting to bypass Windows protections through layered archives. The remediation is designed to restore the intended security posture for users who rely on MotW as part of the default safeguards against untrusted content, particularly for files downloaded from the Internet or from network shares.
What users should do now
Given the seriousness of this zero-day threat, Windows users and administrators are urged to verify that they are running the latest 7-Zip release, specifically version 24.09 or newer. Updating to the fixed version closes the vulnerability path that allowed the bypass of MotW protections via double-encapsulated archives. In addition to updating 7-Zip, practitioners should maintain system hygiene by applying operating system security updates, enabling prompt patches for Windows Defender and related security features, and exercising caution with archives obtained from untrusted sources or received through email, especially when the content appears to be double-archived or uses obfuscated filenames and homoglyphs.
Targeting, delivery, and the phishing ecosystem
How attackers leveraged legitimate-looking channels
The campaign’s success depended on the combination of technical exploitation with social engineering. By using emails that appeared to originate from compromised accounts tied to real Ukrainian institutions, the attackers increased the likelihood that recipients would engage with the attachments. The use of compromised credentials and the impersonation of legitimate entities leveraged existing trust relationships, reducing suspicion and encouraging action. This technique illustrates how threat actors blend cyber exploits with familiar, credible communication channels to improve their chances of success in phishing operations.
The role of homoglyph-based disguises in the phishing chain
Homoglyphs served as a crucial tactic to disguise the nature of the payload. By presenting executable files with extensions and names that resemble ordinary documents, attackers sought to mislead recipients into treating the attachment as a harmless file. This deception is particularly effective when combined with the MotW bypass, as it targets both user perception and automated security checks. The combination of visual trickery and technical exploitation creates a multi-layered risk that is challenging to detect with conventional defenses alone.
Victims and impact considerations
The campaign’s apparent aim was to compromise several organizations that play a role in public administration, infrastructure, and essential services. While the full scope of impact remains under assessment, the potential consequences include unauthorized access to systems, disruption of services, and exposure of sensitive data. The targeting strategy highlights how state-affiliated or governance-focused entities can become focal points for high-stakes cyber operations, particularly when adversaries seek to undermine public confidence or degrade operational capabilities during periods of geopolitical tension.
Broader implications for security and defense strategies
Implications for archiving tools and file security
The 7-Zip vulnerability underscores a broader lesson about the security of widely used tools that handle untrusted content. Archiving utilities frequently operate as gatekeepers for data transfer and storage, and any weakness in how they manage nested content or propagate security attributes across layers can create a systemic risk. The incident demonstrates the importance of rigorous testing of edge cases, such as nested or multi-archive scenarios, and the need for robust mechanisms to propagate security policies and metadata consistently through all levels of data packaging.
Email security, phishing resilience, and user education
The campaign also reinforces the necessity of comprehensive phishing defenses and user education. Even with strong technical safeguards, attackers may exploit human factors by leveraging familiar institutions and legitimate-looking communications. Security programs should emphasize layered defenses, including advanced email filtering, attachment sandboxing, and user awareness training focused on recognizing unusual archive structures, suspicious filenames, and requests to open or extract attachments. The integration of human-centric training with technical controls is critical to reducing the risk posed by social engineering techniques in tandem with file-based exploits.
Defensive posture and policy considerations
From a policy and operational perspective, the incident suggests that security teams should prioritize rapid patch management, timely version updates for software dependencies, and rigorous risk assessments of tools that handle externally sourced content. Organizations should implement incident response playbooks that include procedures for verifying authenticity, isolating affected systems, and restoring integrity after detection of suspicious file packs. As geopolitical tensions influence threat landscapes, maintaining a proactive and adaptive security posture becomes essential to reducing exposure to sophisticated, multi-stage campaigns.
Victimology, indicators, and ongoing monitoring
Indicators of compromise and detection opportunities
Detecting this campaign hinges on a combination of indicators, including the distribution patterns of double-archived files, metadata anomalies in archives, and behavioral signals associated with double-layer extraction attempts. Security teams should monitor for unusual archive nesting, mismatches between outer archive tags and inner content, and the use of characters that resemble common ASCII letters in file names or extensions. In addition, organizations should scrutinize emails that purport to originate from trusted institutions but exhibit atypical attachment structures or naming conventions that suggest obfuscated or deceptively encoded content.
Defensive improvements and monitoring best practices
To bolster resilience, defenders should ensure that all relevant software is up to date with the latest security patches. Monitoring solutions should be tuned to alert on suspicious file packaging patterns, abnormal extraction workflows, and potential attempts to bypass MotW protections. Organizations may consider implementing stricter controls around the handling of archive files, including sandbox execution for suspicious archives, enhanced whitelisting for known-good archives, and prompt user prompts for actions that could result in the execution of content retrieved from the Internet.
Conclusion
The discovery of a zero-day vulnerability in the 7-Zip archiving utility that allowed a Russian cybercrime group to bypass MotW protections during the Ukraine-related conflict highlights the evolving complexity of modern cyber threats. The weakness lay in the improper propagation of Mark of the Web protections to content contained within double-encapsulated archives. By exploiting this gap, attackers could embed malicious payloads inside nested archives and rely on homoglyph-based disguises to improve their chances of delivery, often leveraging compromised credentials from legitimate organizations to increase credibility and reach. The subsequent fix in version 24.09 restored protective safeguards by ensuring MotW coverage extended to all nested content, mitigating the core vulnerability and reducing the risk to Windows users who rely on 7-Zip for archiving tasks.
This incident reinforces the critical need for proactive patch management, robust email and attachment screening, and user education about sophisticated phishing tactics that combine social engineering with technical exploitation. Organizations should continue to monitor for indicators of compromise related to archiving exploits, implement layered defenses, and maintain a vigilant posture as the threat landscape evolves in the context of geopolitical strife. By combining software updates, policy hardening, and informed user practices, defenders can strengthen resilience against multi-stage campaigns that hinge on the interplay between file formats, metadata, and human behavior.
