Patch Ruby uri Gem to Fix Credential Leakage CVE-2025-61594

A newly disclosed vulnerability in the widely used Ruby URI library — tracked as CVE-2025-61594 — reopens a previously patched avenue for credential leakage by bypassing the fix for CVE-2025-27221 and allowing sensitive userinfo (username/password) to leak when URIs are combined using the + operator. This regression affects multiple released versions of the uri gem and the copies bundled with Ruby releases, and it has been fixed in the upstream gem releases 0.12.5, 0.13.3, and 1.0.4 (or later).

Background / Overview​

The uri standard library (distributed as the uri gem in modern Ruby packaging) provides parsing, merging, and manipulation utilities for Uniform Resource Identifiers (URIs). Historically, a prior vulnerability (CVE-2025-27221) allowed authentication credentials embedded in URIs (the userinfo portion) to be retained across host modifications performed by merging or joining operations — a behavior contrary to RFC 3986 expectations and a clear privacy risk when code manipulates untrusted or concatenated URIs. The recent CVE-2025-61594 is not a brand-new class of bug but rather a bypass of previously applied fixes: certain usage patterns — specifically the use of the + operator to combine URIs — can still cause credentials to persist and be copied into a resultant URI. Multiple vendor and community advisories document the regression and the fixes. The Ruby project published an advisory identifying the issue and recommending upgrades to patched gem versions; independent advisory aggregators and package-security systems mirror the same guidance and list the exact patched versions and affected version ranges.

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Why this matters: the risk of URI-embedded credentials​

• URIs with embedded credentials look like this: [url]https://user:password@example.com/path[/url]. Although embedding credentials in URIs is discouraged, it appears in practice in legacy code, test harnesses, service endpoints, and occasionally in configuration strings or scripts.
• When URI manipulation APIs unexpectedly retain or copy the userinfo component, secrets intended only for the original host can be written into new URIs that point at other hosts or services — potentially causing accidental credential disclosure to logs, telemetry, or remote services.
• The vulnerability is particularly problematic in chaining or concatenation operations (e.g., base_uri + path_uri) performed by middleware, HTTP clients, or templated URL generators where developers assume the resulting URI is a safe, host-specific combination.

Exfiltration vectors are straightforward: if an application constructs a forwarding URL, rewrites a callback, or repoints an endpoint by combining URIs, the leaked credentials may appear in cleartext in headers, request lines, or external logs. Because the leak happens in library-level URI combination logic, application-layer sanitization is often bypassed unless developers specifically audit for this behavior.

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A technical look: how the regression happened (what changed)​

Analysis of the upstream uri repository commits linked to the advisory shows focused changes to the way userinfo is assigned and how setter methods behave when parts of a URI are changed. One key change reorders initialization and setter calls and adjusts set_user semantics so that the password is cleared when a new user is set without passing a password explicitly. These changes are directly tied to preventing unintentional retention of the @password internal field during URI merges/concatenations. The relevant upstream commits show diffs to lib/uri/generic.rb and include changes such as moving the set_userinfo call after host/port assignments and ensuring set_user clears the password when appropriate. This is the code-level correction that prevents the + operator from copying an old password into a newly formed URI. Important technical notes:

• The vulnerability specifically triggers when code uses the + concatenation operator between URI objects (or equivalent operations that internally route through the same merge logic).
• The fix modifies internal ordering and setter behavior so that when the host changes (or when userinfo is not intended to be carried over), the password value is not silently preserved.
• The change is implemented across multiple maintained branches of the library, and patched gem releases were published to give users multiple upgrade paths depending on the uri series they use.

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Affected packages, Ruby releases, and patched versions​

The vulnerability affects the uri gem in specific ranges and any Ruby distributions that bundle those versions:

• Affected uri gem versions:
• All versions before 0.12.5
• Versions starting from 0.13.0 and before 0.13.3
• Versions starting from 1.0.0 and before 1.0.4
• Patched uri gem versions:
• 0.12.5
• 0.13.3
• 1.0.4 and later

Community advisories and the GitLab Advisory Database additionally note how the uri gem versions map to Ruby release series: for example, uri 0.12.4 and earlier is bundled in the Ruby 3.2 series; 0.13.2 and earlier bundling appears in Ruby 3.3 series; and 1.0.3 and earlier are bundled in Ruby 3.4 series. In practical terms this means that applications running stock Ruby installations in those series should assume the embedded uri library may be vulnerable unless the system Ruby or gem has been updated.

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Impact and severity — what the scores say​

Different sources show slight variation in severity assessments:

• The GitLab advisory lists a CVSS vector indicating a network-accessible issue with a low-to-medium impact on confidentiality only (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N), assessing the impact primarily to confidentiality (credential leakage).
• Some package-maintainer pages and distribution trackers mark the impact as Low/Medium, and vendor pages that estimate local exploit complexity provide slightly different vectors; always treat these scores as guidance, not absolutes.

In plain terms: the bug is a credential exposure issue and not a remote code-execution bug. The risk is real where applications use embedded credentials or construct URIs programmatically — especially in automated systems, CI pipelines, or multi-tenant platforms where a leaked credential could grant unintended access to services. The exploit complexity depends on whether a vulnerable code path receives attacker-controlled or attacker-influenced inputs.

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Why Windows developers and administrators should care​

Although this is a Ruby library issue, Windows shops are not immune:

• Ruby is commonly used on Windows for tooling, scripts, development servers, and CI runners. Embedded Ruby is also used in many cross-platform tools that run on Windows.
• Windows Subsystem for Linux (WSL) environments often run Ruby apps under Windows-controlled environments; those apps inherit whatever uri gem version is installed in the WSL distro.
• Container images and build artifacts created on Windows or by Windows-based CI/CD runners can carry vulnerable gem versions into production.
• Many organizations run heterogeneous stacks; a Ruby-based microservice collocated with Windows services can leak credentials that impact Windows-hosted resources.

Because the vulnerability’s effect is data leakage — not code execution — the worst outcomes are credential compromise, lateral movement, or delegation issues that can impact services across a mixed OS environment.

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Practical detection and mitigation steps (immediately actionable)​

Short-term: neutralize or block the easiest exploitation paths.

• Inventory and identify:
• Check Gemfile.lock and gems lists for the uri gem version.
• Commands to check locally (Windows PowerShell, WSL, or CMD with Ruby installed):
• ruby -v
• gem list uri --local
• bundle list | Select-String uri (or inspect Gemfile.lock)
• Patch/upgrades (recommended):
• For applications using Bundler:
• Update Gemfile constraints if it pins uri.
• Run bundle update uri or bundle update to pick the patched release.
• For direct gem installs:
• Run gem install uri -v '>= 1.0.4' (or the appropriate patched version for your series).
• If the uri gem is bundled in your Ruby distribution, update Ruby to a release that ships the patched uri, or apply a separate gem install override and ensure your environment picks it up.
• Code scanning and quick fixes:
• Search your codebase for patterns that combine URIs:
• URI#+, URI.join, URI#merge, or custom concatenation wrappers.
• Replace dangerous patterns with explicit, audited logic that does not copy userinfo. For example, if building target URIs, explicitly set or clear uri.user and uri.password after constructing a new URI.
• Sanitization: before logging or emitting URIs, ensure you call uri.user = nil and uri.password = nil where appropriate.
• CI/CD & dependency scanning:
• Add or update dependency scanning rules (Snyk, Dependabot, GitLab Dependency Scanning) to flag uri versions in the vulnerable ranges.
• Ensure containers, build images, and artifacts are rebuilt with the patched gem and that base images are refreshed to include fixes.
• Secrets hygiene:
• Rotate any credentials that may have been exposed or possibly exposed in logs or artifacts and treat exposures conservatively.
• Put secrets into secure storage (e.g., Vault, Azure Key Vault, AWS Secrets Manager) instead of embedding them into URIs.

These steps provide immediate remediation and containment. The primary long-term remedy is an explicit upgrade to a fixed uri gem release and a code review to eliminate practices that embed credentials into URIs.

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Recommended remediation checklist for organizations​

• Immediate (0–48 hours):
• Identify all projects and environments with vulnerable uri versions (scan repos and artifact manifests).
• Deploy patched uri gem versions (0.12.5, 0.13.3, or 1.0.4+) or upgrade Ruby if the gem is bundled.
• Search logs and artifact repositories for patterns like user: or username: in URIs and rotate any possibly exposed credentials.
• Short-term (3–14 days):
• Add SCA tools to CI to block merges that introduce vulnerable uri versions.
• Add a code-quality rule to disallow embedding credentials in URIs and require explicit secret storage.
• Notify internal teams that use Ruby runtimes on Windows, macOS, Linux, and in containers.
• Long-term (weeks to months):
• Harden library usage with linting checks and compile-time guards where feasible.
• Revisit any libraries or projects that expect URI to propagate userinfo and correct assumptions.
• Re-audit the supply chain for third-party gems that depend on uri and ensure they’re also updated.

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Detection guidance: search queries and heuristics​

• Static search patterns in code:
• /URI+\s*/ or code that calls uri +
• URI.join( and URI#merge usage
• Regular expressions for https?://[^/][I]:[^@][/I]@ — look for user:password@ in files and logs
• Runtime diagnostics:
• Introduce a monitoring rule to detect outbound HTTP requests that contain @ with colon-separated credentials in the host portion.
• Audit logs, telemetry, and forwarded request URIs for userinfo fragments.
• Dependency scanning:
• Ensure your SCA tool flags any uri versions in the ranges noted above; update suppression/allow lists accordingly.

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Why the MSRC page may have been unavailable or confusing (user report)​

A check of the Microsoft Security Response Center (MSRC) vulnerability page for CVE-2025-61594 shows that either the page rendering requires JavaScript or the entry is not visible in the plain HTML snapshot — which can lead to “page not found” behavior when accessed by some automated tools or when the page is expected to exist but MSRC does not list third-party, non-Microsoft product CVEs in the same way. MSRC’s tooling and blog emphasize publishing machine-readable CSAF files and CVE data, but differences in catalogue policies mean not every external CVE will have a full MSRC product bulletin in the same way as Microsoft product CVEs. Rely on vendor (Ruby) and community advisories for library-level details in this specific case. Note: Because MSRC focuses primarily on Microsoft product vulnerabilities, the absence of a user-friendly MSRC page should not be interpreted as an indication that the CVE is unimportant; rather, follow the Ruby project advisory and independent security databases for actionable guidance.

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Critical analysis: strengths of the response and remaining risks​

What the community and maintainers did well:

• The Ruby core team and maintainers have issued targeted fixes across multiple uri branches and released patched gem versions promptly after the issue was disclosed.
• The fix is surgical: it corrects the internal assignment and setter semantics to ensure userinfo is not inadvertently carried between URIs, which addresses the root cause without broad API regression.
• Public advisories (Ruby project, RubySec, GitLab advisory database) provide clear guidance on patched versions and recommended upgrades, making remediation straightforward.

Remaining risks and limitations:

• The vulnerability is a regression on a previously fixed class of bug, which raises process concerns: regressions that reintroduce credential leakage indicate a need for improved fuzzing, regression tests, and stricter semantic tests around userinfo handling.
• Not all environments will automatically pick up a patched gem. Systems that use the OS-provided Ruby, vendor-locked images, or legacy application containers may remain vulnerable until images and distributions are refreshed or Ruby is updated.
• Detection of past exposure is non-trivial: leaked credentials may have been forwarded to remote services or recorded in logs/archives before teams were aware of the vulnerability, so a conservative approach — rotating credentials and auditing logs — is required.
• Variation in CVSS scoring between trackers can produce inconsistent prioritization in large enterprises; treat this CVE as a medium-priority confidentiality risk for teams with embedded credentials usage.

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Developer best practices to avoid similar issues​

• Avoid embedding credentials in URIs. Use dedicated secret stores and HTTP authentication headers (e.g., Authorization) that are set at request time rather than encoded into URIs.
• When manipulating URIs programmatically:
• Prefer building URIs from components and explicitly set or clear user and password members.
• Add unit tests that assert userinfo is not preserved when host or authority is changed.
• Add regression tests that detect the specific CVE patterns (e.g., tests that create a URI with userinfo and then combine it with another URI; verify the result has no userinfo).
• Use dependency scanning and lockfiles to reduce the chance of inadvertent library regressions being pulled into builds.

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Final recommendations​

• Upgrade immediately to a patched uri gem version (0.12.5, 0.13.3, or 1.0.4+) or update Ruby distributions that include the patched gem.
• Audit code for any usage of URI#+, URI.join, or URI#merge and sanitize userinfo in any composed URIs.
• Rotate credentials that may have been exposed or might have been logged before the fix was applied.
• Add SCA checks to your CI/CD pipeline to detect vulnerable uri versions and prevent new deployments with the vulnerable packages.
• Treat this issue as a reminder to remove credential embedding in URIs entirely and to harden regression testing around secrets leakage.

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This vulnerability underlines a persistent truth in software security: small, subtle library behavior changes can produce outsized exposure risks when they interact with real-world developer patterns and legacy practices. The technical fix is straightforward and available, but operational remediation requires coordinated dependency updates, code review, and secrets hygiene across development and runtime environments — including Windows-based builds, WSL environments, and container images built on Windows runners. Prompt upgrades, careful log review, and a conservative approach to potentially exposed credentials will reduce the practical risk to organizations.

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Source: MSRC Security Update Guide - Microsoft Security Response Center