Critical Fedora 42 Security Update: mapcidr Tool Patched for Nine High-Severity Go Vulnerabilities

 

Fedora 42 has issued a critical security advisory (FEDORA-2025-73b0006102) for the mapcidr network utility, patching nine vulnerabilities including memory leaks and cross-origin bypasses. This guide details the CVEs—CVE-2025-58058, CVE-2025-47910, and more—their impact on network security and penetration testing, and the essential steps for remediation to protect your systems.

Why a Niche Network Tool Demands Enterprise-Level Attention

In the intricate ecosystem of cybersecurity tools, utilities that operate silently in the background often form the critical backbone of both defensive and offensive security operations. 

The recent Fedora 42 security advisory for golang-github-projectdiscovery-mapcidr is a stark reminder of this reality. 

This update patches a suite of nine vulnerabilities embedded within a popular Go-based CIDR manipulation tool, exposing the hidden risks in foundational software components. 

For security professionals, DevOps engineers, and cloud architects, understanding this advisory is not just about applying a patch; it's about comprehending how supply-chain vulnerabilities in a seemingly simple utility can cascade into significant security events, potentially affecting asset discovery, threat intelligence, and penetration testing workflows.

What is Mapcidr? The Unsung Hero of Network Operations

Before dissecting the vulnerabilities, it's crucial to understand the tool at the center of this storm. Mapcidr, developed by ProjectDiscovery, is a powerful command-line utility and library written in Go. 

Its primary function is to perform complex operations on subnet and CIDR (Classless Inter-Domain Routing) ranges.

Core functionalities include:

• CIDR Expansion & Slicing: Generating all IP addresses within a range or splitting large networks into manageable subnets.

• IP Aggregation: Combining multiple IPs or CIDRs into the smallest possible subnet blocks.

• Filtering and Matching: Isolating specific IPs from within a range.

• Format Conversion: Handling both IPv4 and IPv6 addresses.

In practice, mapcidr is indispensable for security tasks like:

• Attack Surface Mapping: Enumerating all possible targets within a corporate network range.

• Load Distribution: Dividing scan targets for parallelized security assessments.

• Data Processing: Cleaning and organizing large sets of IP addresses for threat intelligence feeds.

Its integration into automated pipelines and other security tools means a vulnerability in mapcidr can have a ripple effect far beyond its immediate use.

Deep Dive: The Nine Vulnerabilities Patched in This Update

The Fedora 42 update to mapcidr version 1.1.97 addresses nine distinct Common Vulnerabilities and Exposures (CVEs). These are not flaws in mapcidr's own code, but in the Go language libraries it depends upon, highlighting the importance of transitive dependency management.

1. Memory Corruption & Resource Exhaustion Flaws

• CVE-2025-58058 (CVSS 5.3 - MEDIUM): A memory leak in the github.com/ulikunitz/xz library. When decoding a corrupted LZMA stream (a compression format), the library fails to detect malformed headers early, leading to unnecessary memory allocation that is not freed. In server environments processing numerous archives, this could lead to gradual memory exhaustion.

• CVE-2025-11579: An Out-of-Memory crash vulnerability in a RAR decoding component.

• CVE-2025-58183 & CVE-2025-58185: Issues related to unbounded memory allocation when parsing specific malformed inputs (GNU sparse maps and DER payloads, respectively).

2. Logic & Security Bypass Flaws

• CVE-2025-47910 (CVSS 5.4 - MEDIUM): A critical logic flaw in Go's net/http.CrossOriginProtection function. The AddInsecureBypassPattern method could inadvertently bypass protection for more requests than intended, potentially allowing Cross-Site Request Forgery (CSRF) attacks to succeed where they should be blocked.

• CVE-2025-47906: A vulnerability in os/exec.LookPath. If the system's PATH variable contains entries that are executable files (not directories), calling LookPath with empty ("") or dot (".") arguments could cause it to incorrectly return one of those executables. This could lead to command injection or privilege escalation in applications that rely on secure path lookup.

3. Information Disclosure & Stability Issues

• CVE-2025-58189: An ALPN negotiation error in crypto/tls that could leak attacker-controlled information.

• CVE-2025-61723: A quadratic complexity issue in encoding/pem that could cause denial-of-service through CPU exhaustion when parsing invalid PEM files.

• CVE-2025-58188: A panic (crash) in crypto/x509 when validating certificates with DSA public keys.

Impact Analysis: Beyond the CVSS Score

The collective impact of these vulnerabilities extends beyond their individual severity scores. For users of mapcidr, the risks are multifaceted:

• Compromised Scan Integrity: A crash (panic) or memory exhaustion during a large-scale network enumeration could halt critical security assessments, causing operational downtime.

• Secondary Attack Vector: If mapcidr is used within a web application or API for network management, the HTTP cross-origin bypass (CVE-2025-47910) could open a secondary attack surface.

• Supply Chain Poisoning: As mapcidr is often a dependency in larger toolchains, these vulnerabilities inject risk into every tool that incorporates it, a classic software supply chain attack scenario.

Remediation and Best Practices for Secure Network Tooling

The immediate remediation path is straightforward but must be executed promptly.

Step 1: Apply the Fedora Update

On Fedora 42 systems, install the update using the command referenced in the advisory:

bash

sudo dnf upgrade --advisory=FEDORA-2025-73b0006102

This will update the golang-github-projectdiscovery-mapcidr package to version 1.1.97-1.fc42, which contains the patched libraries.

Step 2: Broader Environment Assessment

• For Go Developers: Audit your own Go projects. Update your go.mod to use patched versions of the affected libraries (ulikunitz/xz v0.5.14+, Go 1.25.1+ for standard library fixes).

• For Security Teams: Inventory all tools in your arsenal that may embed or depend on mapcidr (e.g., other ProjectDiscovery tools, custom scripts) and ensure they are using the updated version.

• Proactive Monitoring: Subscribe to security feeds for Go and your Linux distribution. Tools like govulncheck can be integrated into CI/CD pipelines to automatically detect vulnerable dependencies.

The Bigger Picture: Trends in Open-Source Security

This advisory is a microcosm of larger trends in 2025:

1. The Language Supply Chain is a Target: Attackers are increasingly focusing on core libraries and languages (Go, Python, JavaScript/Node.js) to maximize the impact of a single vulnerability.

2. Memory Safety Remains Paramount: A significant portion of these CVEs (memory leaks, allocations) are related to memory safety, reinforcing the industry's push towards memory-safe languages.

3. Distribution Maintainers are First Responders: Linux distributions like Fedora play a crucial role in curating, patching, and rapidly disseminating fixes to the ecosystem, often ahead of upstream language releases.

Frequently Asked Questions (FAQ)

Q: I'm not using Fedora. Am I affected?

A: Yes, potentially. The vulnerabilities are in the Go libraries. If you use mapcidr or any Go application that depends on the affected libraries (ulikunitz/xz, Go stdlib < 1.25.1) on any operating system, you should update those dependencies.

Q: Is this vulnerability being actively exploited?

A: The advisory does not mention active exploitation. However, the public disclosure of CVEs often triggers exploit development. Prompt patching is the best defense.

Q: Can I mitigate these issues without updating?

A: For most end-users, no. The fixes require code changes in the libraries. The only reliable mitigation is to apply the update.

Q: Is mapcidr itself insecure?

A: Not inherently. The flaws were in its dependencies. This event highlights the importance of choosing tools with active maintainers who respond quickly to such issues, as the ProjectDiscovery team has done.

Q: What other tools might be affected by these same Go library CVEs?

A: Hundreds of other Go projects. You should check your entire Go toolchain. The CVEs specifically mention other packages like apptainer that were also affected.

Conclusion: Vigilance in the Dependency Tree

The Fedora 42 update for mapcidr is a textbook case in modern cybersecurity hygiene. It underscores that security is a layered endeavor, requiring vigilance not only in your own code but deep within your dependency tree. 

For organizations leveraging open-source tools for network security and operations, this incident serves as a call to action: implement robust software composition analysis (SCA), maintain a timely patching cycle, and develop a deep understanding of the tools that form the bedrock of your security infrastructure. 

Staying secure means looking beyond the headline functionality and into the foundational libraries that make it all possible.

Action: 

Review your systems today. Check for the golang-github-projectdiscovery-mapcidr package or any direct use of mapcidr. Apply the available patches, and use this moment to audit the dependency health of your other critical security tools.