GHSA-qw24-gh76-8rvv BIT-rclone-2026-49980 CVE-2026-49980 GO-2026-5596
Rclone: Unauthenticated command execution in `rclone rcd --rc-serve` via inline remote instantiation, bypassing CVE-2026-41179 fix
Critical
Go
- Severity
- 9.8 / 10
- Critical · CVSS 3.1
- Exploit chance (EPSS)
- 0.78%
- Chance of exploitation in the next 30 days. Higher than 55.96% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-306 Missing Authentication for Critical Function
- CWE-78 Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
- Fix
1.74.3- Upgrade github.com/rclone/rclone to this version or later
Description
Summary
rclone rcd --rc-serve accepts unauthenticated GET and HEAD requests to paths of the form:
/[remote:path]/object
The remote value is parsed from the URL and passed to normal backend initialization. Inline remote configuration can set backend options that execute local commands during initialization. As a result, a single unauthenticated GET or HEAD request can execute a command as the rclone process user.
Versions from 1.55.0 onwards are vulnerable to command execution. Earlier versions (from 1.46.0) are vulnerable to the unauthenticated local file read described under "Additional impact" but not to command execution, because inline backend option overrides did not exist until 1.55.0.
Preconditions
Preconditions for this vulnerability are:
- The rclone remote control API must be enabled, either by the
--rcflag or by running therclone rcdserver - The remote control API must be reachable by the attacker - by default rclone only serves the rc to localhost unless the
--rc-addrflag is in use - The rc must have been deployed without global RC HTTP authentication - so not using
--rc-user/--rc-pass/--rc-htpasswd/etc - The
--rc-serveflag must be in use
Impact
An unauthenticated network attacker who can reach the RC HTTP listener can execute commands as the rclone process user.
Additional impact observed during testing:
GETandHEADboth trigger backend initialization.- The same path allows unauthenticated local file read through inline
localremotes. - Inline
global.*options can mutate process-wide rclone configuration, includingglobal.http_proxy. - Browser subresource requests can also trigger the issue against a localhost-only RC listener. In testing, Firefox triggered the payload from a public HTTPS page containing only an
<img>tag pointing athttp://127.0.0.1:5572/.... This is an additional impact multiplier, not the primary attack precondition.
Mitigations / Workarounds
- Upgrade to rclone 1.74.3 (or 1.75.0 when released).
- Or, configure HTTP authentication on the rc with
--rc-user/--rc-passor--rc-htpasswd, which has always been the recommended deployment. - Or, do not use
--rc-serveif file serving is not needed.
The Fix
The vulnerabilities in this advisory have been fixed by two commits:
- rc: fix unauthenticated command execution via
--rc-serveinline remotes - rc: stop
global.*connection string options changing config
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/ncw/rclone | >= 1.46.0 |
No fix yet |
| github.com/rclone/rclone | >= 1.46.0, < 1.74.3 |
1.74.3 |
| github.com/rclone/rclone | >= 1.49.0, < 1.74.3 |
1.74.3 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/rclone/rclone Go → 1.74.3
- go
go get github.com/rclone/rclone@v1.74.3 && go mod tidy
Severity breakdown
CVSS 3.1 9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
CWE-306: Missing Authentication for Critical Function
The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.
How to prevent it
- Architecture and Design: Divide the software into anonymous, normal, privileged, and administrative areas. Identify which of these areas require a proven user identity, and use a centralized authentication capability. Identify all potential communication channels, or other means of interaction with the software, to ensure that all channels are appropriately protected, including those channels that are assumed to be accessible only by authorized parties. Developers sometimes perform authentication at the primary channel, but open up a secondary channel that is assumed to be private. For example, a login mechanism may be listening on one network port, but after successful authentication, it may open up a second port where it waits for the connection, but avoids authentication because it assumes that only the authenticated party will connect to the port. In general, if the software or protocol allows a single session or user state to persist across multiple connections or channels, authentication and appropriate credential management need to be used throughout.
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Architecture and Design: Where possible, avoid implementing custom, "grow-your-own" authentication routines and consider using authentication capabilities as provided by the surrounding framework, operating system, or environment. These capabilities may avoid common weaknesses that are unique to authentication; support automatic auditing and tracking; and make it easier to provide a clear separation between authentication tasks and authorization tasks. In environments such as the World Wide Web, the line between authentication and authorization is sometimes blurred. If custom authentication routines are required instead of those provided by the server, then these routines must be applied to every single page, since these pages could be requested directly.
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using libraries with authentication capabilities such as OpenSSL or the ESAPI Authenticator [REF-45].
- Implementation, System Configuration, Operation: When storing data in the cloud (e.g., S3 buckets, Azure blobs, Google Cloud Storage, etc.), use the provider's controls to require strong authentication for users who should be allowed to access the data [REF-1297] [REF-1298] [REF-1302].
CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.
How to prevent it
- Architecture and Design: If at all possible, use library calls rather than external processes to recreate the desired functionality.
- Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
- Architecture and Design: For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible. For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field.
- Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error.
- Implementation: While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
- Implementation: If the program to be executed allows arguments to be specified within an input file or from standard input, then consider using that mode to pass arguments instead of the command line.
- Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated. Some languages offer multiple functions that can be used to invoke commands. Where possible, identify any function that invokes a command shell using a single string, and replace it with a function that requires individual arguments. These functions typically perform appropriate quoting and filtering of arguments. For example, in C, the system() function accepts a string that contains the entire command to be executed, whereas execl(), execve(), and others require an array of strings, one for each argument. In Windows, CreateProcess() only accepts one command at a time. In Perl, if system() is provided with an array of arguments, then it will quote each of the arguments.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When constructing OS command strings, use stringent allowlists that limit the character set based on the expected value of the parameter in the request. This will indirectly limit the scope of an attack, but this technique is less important than proper output encoding and escaping. Note that proper output encoding, escaping, and quoting is the most effective solution for preventing OS command injection, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent OS command injection, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, when invoking a mail program, you might need to allow the subject field to contain otherwise-dangerous inputs like ";" and ">" characters, which would ne
- Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
- Operation: Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).
- Operation: Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).
- Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not. In the context of OS Command Injection, error information passed back to the user might reveal whether an OS command is being executed and possibly which command is being used.
- Operation: Use runtime policy enforcement to create an allowlist of allowable commands, then prevent use of any command that does not appear in the allowlist. Technologies such as AppArmor are available to do this.
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
- Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
- Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-38xv-hf3p-h7mq rclone: source object names can escape the configured root on upload | Medium | Also affects github.com/rclone/rclone |
| GHSA-2p48-j3qc-rx9f rclone: S3 multipart declared-length memory exhaustion | High | Also affects github.com/rclone/rclone |
| GHSA-p569-5gjg-9cmj rclone: RC per-server auth-proxy bypass | Critical | Also affects github.com/rclone/rclone |
| GHSA-xwwr-4h3p-r22c rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass | Critical | Also affects github.com/rclone/rclone |
| GHSA-c476-6w5q-jw77 rclone: FTP cross-session auth-proxy backend confusion | High | Also affects github.com/rclone/rclone |
| GHSA-f8g7-2xjc-7mfh rclone: Directory metadata (chmod/chown/chtimes) applied through a planted symlink in rclone local --links escapes the destination | High | Also affects github.com/rclone/rclone |
| GHSA-p6m2-r3w9-mpxw rclone local: crafted Range request against a translated symlink panics (DoS) | Medium | Also affects github.com/rclone/rclone |
| GHSA-66hp-wgxq-6f5q rclone archive/zip: Zip Slip via unsanitized zip entry names lets a malicious archive escape its own namespace | Medium | Also affects github.com/rclone/rclone |
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