CVE-2026-15747
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedMojolicious versions from 4.59 before 9.48 for Perl expose a stable representation of the session CSRF token to a BREACH compression oracle. _csrf_token generates and caches one token per session and returns the same value on every call, and _csrf_field places that value in a hidden `csrf_token` input. When a response carrying the token also echoes attacker-controlled input and is gzip-compressed, the chosen values and the resulting compressed lengths form a BREACH oracle. An attacker able to query it can recover the token and pass csrf_protect validation.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceMojolicious CSRF token generation caches a single token per session, returning the same value on every call. When responses containing this stable token are gzip-compressed and also reflect attacker-controlled input, the compressed length differences form a BREACH oracle. Attackers can iteratively guess token characters by observing which guesses produce smaller compressed sizes, eventually recovering the full token and bypassing CSRF protection.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Mojolicious versionRun 'perl -MMojolicious -e 'print $Mojolicious::VERSION'' or check your project's dependency file for the Mojolicious version entryAffected if Version falls within 4.59 through 9.48 inclusive
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Verify gzip compression is enabledInspect your Mojolicious application configuration for 'compress' or 'encoding' settings, or check if middleware like Mojolicious::Plugin::Gzip is loadedAffected if Gzip compression is actively used for HTTP responses
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Confirm CSRF protection is in useCheck your application code for 'csrf_token' or 'csrf_protect' hooks, or look for the Mojolicious::Plugin::CSRFDefault module in useAffected if CSRF token generation is enabled in the application
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Determine CSRF token generation strategyReview your CSRF token generation implementation to see if a single token is reused across the entire session versus generating a fresh token per requestAffected if The application uses a single stable CSRF token per session that persists across multiple requests
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Check if responses with CSRF tokens include user-supplied inputReview response templates and routes that echo back request parameters while also serving CSRF tokensAffected if Responses containing the CSRF token also include attacker-controllable data (query parameters, form input, headers)
You are affected if Mojolicious version is between 4.59-9.48 AND gzip compression is enabled AND your application uses session-stable CSRF tokens in responses that also echo attacker-controlled input.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedThe framework should generate per-request or cryptographically masked tokens instead of caching a single session token, breaking the oracle. Alternatively, disable compression on endpoints that echo user input alongside CSRF tokens.
9.48
- Check current Mojolicious version: perl -MMojolicious -e 'print $Mojolicious::VERSION'
- If version is below 9.48, upgrade using your Perl package manager (cpanm Mojolicious or cpan Mojolicious)
- Verify the upgrade was successful by checking the version again
- Test that CSRF protection continues to function correctly in your application
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,224.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-15747 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-15747 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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