Symfony Security Triage

Decides how a finding is handled, not whether the code is wrong. It complements symfony-security-review (which finds missing hardening) by making the disclosure call on a report.

The three dispositions and the conventions that record them:

Disposition	Label	Branch prefix	Process
CVE	Has CVE + severity	cve-*	Private fix, GHSA/CVE, credit, blog post, coordinated release
Public hardening	none / Not a security issue	harden-*, hardening-*, pin-*, fix-*	Normal open PR, changelog, no embargo
Not a security issue	Not a security issue / Won't fix	n/a or fix-*	Reply to reporter; optionally a doc/robustness PR

This skill produces a recommendation. The final call belongs to the Symfony security team; treat its output as a structured argument, and defer to symfony.com/security for the authoritative "what is not a vulnerability" list.

Progress checklist

• Step 0: Establish the facts (reproduce, scope, trust model)
• Step 1: Apply the disposition decision tree
• Step 2: Assign severity and affected maintained branches
• Step 3: Route (branch prefix, labels, next workflow, reporter reply)

Confirmation rule

Whenever this skill says "Wait for confirmation", treat anything other than an explicit affirmative as no: stop and ask the user how they want to proceed.

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Step 0 — Establish the facts

Before classifying, pin down four things. Guessing any of them produces a wrong call.

1. Reachability: is the vulnerable code on a path reachable from untrusted input in a default configuration, or does it need opt-in/insecure config?
2. Actor and precondition: what must the attacker already have? Unauthenticated and remote is the worst case; "already controls the serialized bytes" or "already has the app secret" usually means the precondition is itself game-over.
3. Impact: RCE, auth/authz bypass, SSRF to internal, signature/secret bypass that accepts forged input, XSS on a default-rendered surface, secret disclosure, open redirect, session fixation, or "only" DoS / info of low value.
4. Contract: is the component meant to defend this boundary (router, HttpFoundation/HttpClient, Security, webhook verification, HtmlSanitizer, Mime parsing), or is the unsafe behaviour documented as the caller's responsibility (deserializing untrusted bytes, a trusted-channel feature such as ESI, template_from_string)?

Reproduce if at all possible; an unreproducible report is not yet triable.

Step 1 — Disposition decision tree

Apply in order. The first matching bucket wins.

It is not a security issue if any of these hold

• Pure DoS / resource exhaustion. Generally excluded from the CVE pipeline. Fix as hardening with a limit if cheap, but no CVE.
• Requires misuse contrary to documentation, with no default-config attack. The component is not contracted to defend this (e.g. deserializing untrusted bytes through an API documented as trusted-only; using a trusted-channel feature to reach internal hosts).
• Dev-only tooling (profiler, debug, web-profiler) manifesting only in a dev environment.
• Precondition is already game-over (attacker already holds the app secret, controls the deserialized input contract, or has local/physical access).
• Not reproducible, or rooted in a third-party dependency outside Symfony's control.
• Not a realistic bypass (a comparison nuance with no working exploit, etc.).

It is a CVE only if all of these hold

1. Default-reachable: exploitable against a default or documented-safe config.
2. Expected actor: the attacker is at or below the trust level the boundary is meant to enforce (typically unauthenticated/remote, or a lower-privileged user escalating), with no game-over precondition.
3. Contracted boundary: the component is meant to defend this (see Step 0.4).
4. Real impact: RCE, auth/authz bypass, SSRF to internal, sanitizer/signature bypass accepting forged input on a sensitive sink, stored/reflected XSS on a default surface, secret disclosure, or open redirect with meaningful reach.
5. Maintained: the vulnerable code ships in a maintained version.

Otherwise it is public hardening

A genuine improvement where a CVE condition fails. Typical shapes:

• Defense-in-depth on top of an existing control, or that only matters once another bug already holds (an __unserialize __toString trampoline guard needs a pre-existing untrusted unserialize() entry to matter).
• Safer-default change where the old default was not a vulnerability under the threat model (adding a webhook IP allowlist, pinning the HMAC algorithm).
• Limited impact or exposure even though a boundary is technically crossed (a forged webhook against an opt-in endpoint with a user-configured secret injects only a delivery-status event).
• Robustness improvements (input-length caps, broader sanitizer coverage).

Step 2 — Severity and affected branches

Severity (match the low/medium/high labels; CVSS is a sanity check, not the goal):

• high: unauthenticated RCE, auth bypass, full sanitizer bypass enabling stored XSS, SSRF reaching internal services.
• medium: reflected XSS, open redirect, signature bypass with bounded impact, info disclosure of non-trivial data.
• low: defense-in-depth, narrow-config or low-impact issues, most hardening.

Affected branches: find the oldest version where the vulnerable code exists, intersect with maintained_versions from https://symfony.com/releases.json. Fix on the lowest maintained affected branch, then merge up (see the symfony-merge-up skill). Record the oldest exposure even if it predates maintained versions.

Step 3 — Route

State the recommendation as: disposition + severity + affected maintained branches + the one-line rationale (which decision-tree conditions decided it), then route:

• CVE: name the branch cve-<slug>-<branch>; apply Has CVE + severity; the fix is prepared privately and goes through the coordinated-disclosure process (request a GHSA/CVE, credit the reporter, prepare the security release and blog post). Do not open a public PR or push to a public remote before release. Wait for confirmation before any outward step.
• Public hardening: name the branch harden-/hardening-/pin-/fix-<slug>; open a normal PR with a CHANGELOG entry; use symfony-security-review to confirm the fix and symfony-hardening-rule to add a durable gate where the class recurs.
• Not a security issue: draft a short, factual reply to the reporter explaining why (cite the contract/threat-model reason), and optionally a doc clarification or low-priority robustness PR. Apply Not a security issue / Won't fix.

In every case, the fix follows TDD, component-scoped tests, no em-dashes, no Claude/Anthropic credit, comments sparingly, no issue references in code.

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Worked examples (abstracted patterns)

Finding shape	Disposition	Deciding factor
SSRF filter (private-network client) bypassed in a default configuration	CVE	default control bypassed, unauthenticated reach
HTML sanitizer lets a javascript: URL through on a default profile	CVE	sanitizer's core contract bypassed, stored XSS
URL generator emits a path that crosses a routing boundary by default	CVE	boundary crossed in default use
A signed transport decodes the payload before verifying its MAC	CVE candidate, high	pre-auth RCE if signing is meant to defend a malicious broker; confirm the trust model
Webhook signature compared with !==, or the secret is ignored	Hardening	opt-in endpoint, user-configured secret, bounded impact
__unserialize assigns a string property without a \Stringable guard	Hardening	needs a pre-existing untrusted unserialize() entry (game-over precondition)
Input-length cap / broader sanitizer coverage added	Hardening	robustness, not a default-exploitable bypass
Unbounded recursion / regex backtracking / cache growth on input	Hardening, low	pure DoS, excluded from the CVE pipeline
Deserializing bytes through an API documented as trusted-only	Not a security issue	documented contract, caller's responsibility
A trusted-channel feature (e.g. ESI/SSI) used to reach internal hosts	Not a security issue	trusted by design
Case-insensitive host allowlist with no working bypass	Not a security issue	not a realistic bypass

Gotchas

• "Boundary crossed" does not imply CVE. Impact and exposure decide it. A forged webhook against an opt-in, user-secret endpoint is hardening; an SSRF filter bypass in default use is a CVE.
• DoS is the most common miscategorisation. Resource exhaustion is hardening/low, not a CVE, even when trivially triggerable.
• Defense-in-depth tells. If exploiting the finding requires another, already-present vulnerability or a leaked secret, it is hardening.
• Trust-model questions are for the maintainer. A signed-transport verify-order case turns on whether the broker is trusted; surface the question, do not assume.
• Embargo discipline. Never name a CVE-bound finding, push a cve-* branch, or open a public PR for a CVE-class finding before the coordinated release. Wait for confirmation.
• Defer to authority. symfony.com/security is the source of truth for what is not a vulnerability; this skill encodes observed practice, not policy.

Error handling

• If reachability or trust model is unknown, say so and triage as needs-human-judgement; do not force a disposition.
• Security reports are handled privately. Do not echo report contents into public artifacts, commit messages, or branch names that leak the vulnerability before release.
• Never push to a public remote during CVE triage. Stop and hand back to the user.