CVE-2026-77647 in SPIP
Summary
by MITRE • 08/21/2026
SPIP before 4.4.20 allows unauthenticated remote attackers to execute arbitrary code, as exploited in the wild in August 2026. This is related to incorrect identification of <?php blocks, and var_export's mishandling of certain cases such as presence of a '<' character.
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Analysis
by VulDB Data Team • 08/21/2026
The vulnerability identified in SPIP versions prior to 4.4.20 represents a critical server-side code injection flaw that allows unauthenticated remote attackers to execute arbitrary PHP code on the target system. This specific weakness stems from an incorrect identification and processing of PHP opening tags within user-supplied input or data structures handled by the application's core functions. The root cause is deeply tied to how the var_export function interacts with certain character sequences, particularly the presence of a less-than symbol '<' in conjunction with other characters that mimic valid PHP syntax. When SPIP processes this malformed input, it fails to properly escape or validate the data before inclusion or evaluation, leading to unintended code execution contexts where attacker-controlled payloads are interpreted as executable script rather than static text.
From a technical perspective, the flaw exploits the nuances of how PHP parses strings and arrays during export operations. The var_export function is designed to return a string representation of a variable that can be evaluated by eval or included in another file. However, if the input data contains specific edge cases involving angle brackets, the internal logic for identifying valid <?php blocks becomes confused. This confusion allows an attacker to inject code fragments that bypass standard sanitization checks because the application incorrectly assumes these sequences are safe or part of a different context. The exploitation does not require any form of authentication, meaning that any user with network access to the SPIP instance can trigger this condition, making it particularly dangerous in public-facing deployments where no login is required for initial interaction.
The operational impact of this vulnerability is severe, as successful exploitation leads to full remote code execution (RCE) on the web server hosting the CMS. An attacker could use this capability to upload malicious scripts, modify existing files, extract sensitive database contents, or pivot further into the internal network infrastructure. Given that SPIP is a widely used content management system for publishing and collaborative writing, compromising its integrity can lead to widespread defacement, data breaches affecting numerous users, and potential denial of service conditions if the server resources are exhausted by malicious activities initiated through this vector. The fact that this vulnerability has been exploited in the wild indicates that automated scanners or targeted attacks may already be actively probing for this weakness in production environments.
To mitigate this risk, organizations running SPIP must immediately upgrade to version 4.4.20 or later, where these parsing inconsistencies have been addressed and input validation mechanisms strengthened. Until an update can be applied, administrators should consider implementing strict web application firewall rules that detect and block attempts to inject PHP tags via query parameters or POST data containing suspicious character sequences like '<' followed by 'php'. Additionally, enabling open_basedir restrictions in the PHP configuration can limit the damage if exploitation occurs by preventing scripts from accessing files outside of designated directories. Regular security audits and patch management cycles are essential to prevent such known vulnerabilities from being leveraged against legacy systems.
This vulnerability aligns with Common Weakness Enumeration (CWE) categories related to improper input validation, specifically CWE-94 which covers Improper Control of Generation of Code or Script, often referred to as code injection. Furthermore, the exploitation technique maps directly to MITRE ATT&CK tactics involving Initial Access and Execution, where attackers leverage application vulnerabilities to gain a foothold in the environment. Understanding these mappings helps security teams prioritize remediation efforts based on standardized frameworks that reflect real-world attack behaviors. By addressing this flaw through software updates and defensive configurations, administrators can significantly reduce their exposure to active exploitation campaigns targeting unpatched SPIP installations.