7 Critical Vulnerabilities in Linux Servers in 2025: Real Risks and Expert Cloud Advice

David Carrero (Stackscale): “Threats are no longer futuristic; they’re everyday. Resilience begins at the core of the system.”

In an increasingly automated, exposed, and multi-cloud landscape, the security of Linux servers in 2025 is at a critical crossroads. Pressure on system and security teams has grown due to the proliferation of sophisticated exploits and the ongoing abuse of known vulnerabilities. Cloud and bare-metal infrastructure are not immune to this reality.

David Carrero, co-founder of Stackscale (Aire Group) and expert on critical platforms, warns: “It’s no longer enough to just patch. We need to redesign how we think about security architecture from the ground up, from firmware to application layers.”

Below, a technical review of the seven most critical vulnerabilities affecting Linux servers this year.

1. Privilege Escalation in SUSE and udisks2 (CVE‑2025‑6018 and CVE‑2025‑6019)

A combined attack chain allows a non-privileged SSH user to become root by exploiting the pam_env module and the udisks2 daemon. This affects SUSE, Ubuntu, Debian, Fedora, and AlmaLinux.

Attack sequence:

1. SSH user manipulates variables like XDG_SEAT.
2. PAM grants the “allow_active” status.
3. Udisks2 allows mounting an XFS image with a SUID-root binary.
4. The attacker executes a shell with root privileges.

Immediate mitigation:

• Apply patches released in June 2025.
• Modify Polkit (auth_admin instead of allow_active).
• Disable user_readenv in SSHD.
• Audit logs for suspicious mount activities.

🗨 David Carrero: “The concern with this vector is that it doesn’t require complex code, just misconfiguration. It’s the type of flaw that jeopardizes critical environments with exposed SSH access.”

2. Remote Execution and MITM in OpenSSH (CVE‑2025‑26465 and CVE‑2025‑26466)

These vulnerabilities, present from OpenSSH 6.8p1 to 9.9p1, allow for SSH connection interception and service denial attacks.

• 26465: man-in-the-middle attack accepting fraudulent keys.
• 26466: malicious packets can crash legitimate sessions.

Solution: upgrade to OpenSSH 9.9p2 or newer.

Recommended enhancements:

• Enable StrictHostKeyChecking.
• Disable insecure algorithms like SHA-1 or CBC.
• Restrict access with AllowUsers.

🗨 David Carrero: “SSH is the main gateway in Linux environments. Without proper audit and restrictions, any attacker can exploit these gaps to hijack production sessions.”

3. Kernel Synchronization Failures (CVE‑2025‑1023 and CVE‑2025‑1087)

Found in kernels 5.15.0-90 and earlier (especially Ubuntu 20.04 and 22.04), these vulnerabilities enable race conditions leading to privilege escalation or denial of service.

Affected environments:

• Ubuntu, Debian, RHEL, Fedora, and derivatives with LTS kernels.

Solution:

• Install patched versions from official repositories.
• Enable hardening options in the kernel (KASLR, CONFIG_DEBUG_RODATA).
• Use tools like AIDE to audit integrity.

4. Spectre-v2 “Training Solo” (CVE‑2024‑28956, CVE‑2025‑24495)

A new speculative attack type on modern CPUs that bypasses traditional mitigations like IBPB and eIBRS.

Risk:

• Kernel memory leakage from user processes.
• Impacts Intel Tiger Lake, Ice Lake, Xeon 2nd–3rd gen, and ARM CPUs.

Mitigation:

• Update microcode (May 2025 or later).
• Install kernels supporting IBHF.
• Isolate multi-tenant workloads in public clouds.

🗨 David Carrero: “This attack shows that hardware isolation alone is no longer enough. Solutions need to be multilayered, combining microcode updates, secure virtualization, and strict segmentation.”

5. Modern SSRF in Cloud Internal APIs

Server-Side Request Forgery (SSRF) vulnerabilities allow attackers to access internal metadata and configurations by manipulating web requests or APIs.

Real cases:

• AWS: IAM token exposure via 169.254.169.254.
• Azure and GCP: metadata endpoint attacks through poorly isolated microservices.

Evading techniques in 2025:

• IP obfuscation (0xA9FEA9FE).
• DNS rebinding.
• Chain attacks with LFI or XXE.

Mitigation:

• Block internal ranges via proxy/firewall.
• Validate URLs against allowlists.
• Limit redirects and response size.
• Use tools like ssrfmap or Burp.

6. New Gaps in Misconfigured Containers

Although not tied to specific CVEs, 2025 has seen an increase in attacks exploiting poorly isolated containers (e.g., unrestrained Docker, --privileged, SUID binaries in volumes).

Common risks:

• Host privilege escalation.
• Access to Docker or Kubernetes sockets.
• Manipulation of images with persistent code.

Recommendations:

• Never run privileged containers in production.
• Enable AppArmor or seccomp.
• Do not expose Docker/Kubelet daemons without TLS.
• Monitor access to /proc, /sys, and virtual devices.

🗨 David Carrero: “In cloud and bare-metal, container security must be supplemented with policies and controls. Tools are available, but few take low-level runtime security seriously.”

7. Compromised or Outdated Repositories

In 2025, several server incidents stem from:

• Use of unsigned third-party APT/YUM repositories.
• Automated scripts installing packages without GPG verification.
• Failures in snap, flatpak, or OCI repositories with infected images.

Preventive measures:

• Use only official signed repositories.
• Enable GPG signature verification.
• Isolate testing and production environments.
• Monitor hashes and unexpected changes with tripwire.

Conclusion

The vulnerabilities of 2025 demonstrate that the attack surface has expanded from the kernel to external layers like APIs, containers, and repositories. Responses must be both technical and strategic.

🗨 David Carrero: “The key isn’t just patches, but visibility. Observability, configuration management, and hardening practices must be integrated from the design phase. That’s the difference between a resilient system and an exposed one.”

In a world where availability and trust are key differentiators, understanding and mitigating these seven critical vulnerabilities can mean the difference between operational continuity and a devastating security incident.