GHSA-mr3q-g2mv-mr4q CVE-2025-61921
Sinatra is vulnerable to ReDoS through ETag header value generation
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- 0.50%
- Chance of exploitation in the next 30 days. Higher than 42.49% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
4.2.0- Upgrade sinatra to this version or later
Description
Summary
There is a denial of service vulnerability in the If-Match and If-None-Match header parsing component of Sinatra, if the etag method is used when constructing the response and you are using Ruby < 3.2.
Details
Carefully crafted input can cause If-Match and If-None-Match header parsing in Sinatra to take an unexpected amount of time, possibly resulting in a denial of service attack vector. This header is typically involved in generating the ETag header value. Any applications that use the etag method when generating a response are impacted if they are using Ruby below version 3.2.
Resources
- https://github.com/sinatra/sinatra/issues/2120 (report)
- https://github.com/sinatra/sinatra/pull/2121 (fix)
- https://github.com/sinatra/sinatra/pull/1823 (older ReDoS vulnerability)
- https://bugs.ruby-lang.org/issues/19104 (fix in Ruby >= 3.2)
Affected versions
RubyGems
| Package | Vulnerable | Fixed in |
|---|---|---|
| sinatra | < 4.2.0 |
4.2.0 |
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.
sinatra RubyGems → 4.2.0
- bundler
bundle update sinatra # Gemfile: gem "sinatra", ">= 4.2.0"
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- Low
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
- Exploit maturity
- Unreported
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Weakness
CWE-1333: Inefficient Regular Expression Complexity
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
How to prevent it
- Architecture and Design: Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
- System Configuration: Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
- Implementation: Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
- Implementation: Limit the length of the input that the regular expression will process.
CWE-400: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How to prevent it
- Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
- Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
- Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
- Implementation: Ensure that all failures in resource allocation place the system into a safe posture.
References
Advisories
Packages
Other links
- github.com/sinatra/sinatra/security/advisories/GHSA-mr3q-g2mv-mr4q
- github.com/sinatra/sinatra/issues/2120
- github.com/sinatra/sinatra/pull/1823
- github.com/sinatra/sinatra/pull/2121
- github.com/sinatra/sinatra/commit/3fe8c38dc405586f7ad8f2ac748aa53e9c3615bd
- github.com/sinatra/sinatra/commit/8ff496bd4877520599e1479d6efead39304edceb
- bugs.ruby-lang.org/issues/19104
- github.com/rubysec/ruby-advisory-db/blob/master/gems/sinatra/CVE-2025-61921.yml
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-hxx2-7vcw-mqr3 Sinatra vulnerable to Reliance on Untrusted Inputs in a Security Decision | Medium | Also affects sinatra |
| GHSA-2x8x-jmrp-phxw Sinatra vulnerable to Reflected File Download attack | High | Also affects sinatra |
| GHSA-qp49-3pvw-x4m5 sinatra does not validate expanded path matches | High | Also affects sinatra |
| GHSA-mq35-wqvf-r23c Sinatra Cross-site Scripting vulnerability | Medium | Also affects sinatra |
| GHSA-h29f-7f56-j8wh Sinatra Path Traversal vulnerability | Medium | Also affects sinatra |
| GHSA-7wch-p9px-956x Forge: Regular expression denial of service in PEM decoding (pem.decode) | High | Same weakness, CWE-1333 |
| GHSA-xcq7-p3pf-p88h OpenTelemetry Python: Unbounded tracestate parsing in opentelemetry-api | Medium | Same weakness, CWE-1333 |
| GHSA-xgh8-jp6q-p5x8 Pillow: ReDoS in XbmImagePlugin: 512-byte file stalls Image.open() for minutes | High | Same weakness, CWE-1333 |
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