CVE-2026-31959: 
NixOS vulnerability analysis and mitigation

CVE-2026-31959 is a Server-Side Request Forgery (SSRF) vulnerability in Anchore Quill, a Go-based tool for macOS binary signing and notarization. It affects all versions of github.com/anchore/quill prior to v0.7.1 and was disclosed on March 10, 2026, via a GitHub Security Advisory. The flaw exists in both the Quill CLI and library when retrieving Apple notarization submission logs. It carries a CVSS v3.1 base score of 5.3 (Medium) (GitHub Advisory, Feedly).

The root cause is improper input validation (CWE-20) and Server-Side Request Forgery (CWE-918): when Quill retrieves Apple notarization submission logs, it fetches a URL returned in the Apple API response without validating that the URL scheme is https or that the target host is not a local, loopback, link-local, or multicast IP address. An attacker positioned to tamper with the API response — for example, via a TLS-intercepting proxy, a compromised certificate authority, or another trust boundary violation — can inject an arbitrary URL into the response. Quill will then issue an HTTP or HTTPS request to that attacker-controlled destination, potentially reaching internal network services or cloud metadata endpoints (e.g., 169.254.169.254). The fix introduced a three-tier URL validator: known Apple/S3 domains are silently allowed, IP addresses and localhost are blocked, and unknown domains are allowed with a warning (GitHub Advisory, Fix Commit).

Successful exploitation can lead to exfiltration of sensitive data, including cloud provider credentials (e.g., AWS instance metadata tokens) and internal service responses, by causing the Quill client to make unauthorized requests to attacker-controlled or internal network destinations. Confidentiality impact is rated High, while integrity and availability are unaffected. The attack vector is adjacent network with high complexity, limiting the practical blast radius, but environments using TLS-intercepting proxies — common in corporate CI/CD pipelines where Quill is typically deployed — face elevated risk (GitHub Advisory, Red Hat Bugzilla).

No public proof-of-concept exploit code or in-the-wild exploitation has been reported for CVE-2026-31959. The EPSS score is approximately 0.02% (6th percentile), indicating a very low probability of near-term exploitation. Exploitation requires a high-complexity precondition — the ability to intercept and modify HTTPS responses from Apple's notarization API — which is not achievable under standard network conditions. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The vulnerability was responsibly disclosed by opera-aklajn of Opera (GitHub Advisory).

1. Identify target environment: Locate a CI/CD pipeline or developer workstation running Quill (versions < 0.7.1) that uses the notarization log retrieval feature and operates behind a TLS-intercepting proxy or in an environment with a compromised CA.
2. Position for interception: Gain the ability to intercept and modify HTTPS responses from appstoreconnect.apple.com — for example, by controlling a TLS-inspection proxy, compromising a CA trusted by the host, or performing an ARP/DNS-based MITM on the adjacent network.
3. Craft malicious API response: Intercept the Apple notarization API response to the Get Submission Log endpoint and replace the legitimate developerLogUrl field value with an attacker-controlled URL (e.g., http://169.254.169.254/latest/meta-data/iam/security-credentials/ for AWS metadata, or an internal service URL).
4. Trigger log retrieval: Ensure Quill executes the notarization log retrieval step (e.g., by running quill notarize or invoking the library's log fetch function), causing it to issue an HTTP/HTTPS request to the injected URL.
5. Collect exfiltrated data: Capture the response from the internal or metadata endpoint, which may include cloud provider credentials, IAM tokens, or sensitive internal service data, at the attacker-controlled server or via the intercepted response (GitHub Advisory, Fix Commit).

• Network: Outbound HTTP or HTTPS requests from the Quill process to unexpected destinations (e.g., 169.254.169.254, RFC 1918 private IP ranges, or non-Apple/non-S3 domains) during notarization log retrieval; unusual DNS queries for internal hostnames originating from CI/CD build agents.
• Logs: Quill log output containing warnings such as unexpected host "<domain>" for developer log URL (introduced in v0.7.1 for unknown domains); HTTP client errors or unexpected successful responses when fetching notarization logs from non-Apple URLs.
• Process: The Quill process making network connections to destinations other than *.apple.com or notary-artifacts-prod.s3.amazonaws.com during the notarization log fetch phase.
• File System: Unexpected credential files or tokens written to disk if an attacker-controlled endpoint returns data that is subsequently processed or cached by the build pipeline (Fix Commit).

Upgrade Quill to version v0.7.1 or later, which introduces URL validation for Apple notarization log responses, blocking IP addresses, localhost, and non-HTTPS schemes while allowing known Apple and S3 domains (Quill v0.7.1 Release). No official workarounds are available for unpatched versions. As a defense-in-depth measure, restrict outbound network access from CI/CD build agents to only known-good Apple and AWS S3 endpoints, and audit TLS inspection proxy configurations to minimize trust boundary exposure (GitHub Advisory).

The vulnerability was credited to opera-aklajn of Opera, who responsibly disclosed it to Anchore. Red Hat tracked the issue via Bugzilla (Bug 2446750) and assigned it medium severity. No significant broader media coverage or notable researcher commentary beyond the official advisory has been identified (GitHub Advisory, Red Hat Bugzilla).