How severe is CVE-2026-49212?

No CVSS score has been assigned to CVE-2026-49212 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-49212?

CVE-2026-49212 affects the following packages: symfony/ux-live-component (Packagist), symfony/ux-live-component (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-49212?

Update symfony/ux-live-component to 2.36.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49212 is resolved across your whole dependency graph.

How do I detect CVE-2026-49212 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/ux-live-component, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-49212 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-49212 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-49212 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-49212?

CVE-2026-49212 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 14th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-49212?

CVE-2026-49212 is classified as CWE-345 (CWE-345). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-49212 published, and has it been updated?

CVE-2026-49212 was published on July 17, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

CVE-2026-49212 — ux-live-component

Fix: symfony/ux@a224b5a

CVE-2026-49212 is a CWE-345 vulnerability in symfony/ux-live-component. A fix is available for symfony/ux-live-component — see the affected versions and patch details below.

Symfony UX: LiveComponentHydrator HMAC checksum lacks component and slot binding

Also known asGHSA-34w5-c283-j9fg

Published

Jul 17, 2026

Updated

Aug 12, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 15, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-49212.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs14th percentile — riskier than 14% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

🐘symfony/ux-live-component🐘symfony/ux-live-component

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

In symfony/ux-live-component, a component's server-side state is exposed to the browser as a set of props (#[LiveProp]-annotated properties). Props marked writable: true can be freely changed by the client. Read-only props are round-tripped to the browser and back, and their integrity is protected by an HMAC so the client cannot tamper with them. Child components additionally receive a propsFromParent blob, also HMAC-signed.

The HMAC computed by Symfony\UX\LiveComponent\LiveComponentHydrator covered only the sorted prop key/value pairs. It didn't include the component name, the slot identifier (props vs propsFromParent), or any request context, and a single application-wide secret is used for every component. A signed blob the server minted for component A is therefore a valid signature for component B if the key names happen to match, and a props blob can be replayed in the propsFromParent slot (or the reverse). An attacker can use this to set a read-only prop on a target component to a value they were only ever allowed to choose as a writable prop on another component.

Resolution

The HMAC is now bound to its context: the component name and a slot identifier are included in the pre-image before hashing. Two constants (CHECKSUM_SLOT_PROPS and CHECKSUM_SLOT_PROPS_FROM_PARENT) name the two slots, and calculateChecksum(), verifyChecksum(), addChecksumToData(), and ChildComponentPartialRenderer thread these values through. Cross-component and cross-slot replays no longer verify.

The patch for this issue is available here for branch 2.x (and forward-ported to 3.x).

Credits

Symfony would like to thank Anthropic (via Project Glasswing) for reporting the issue and Hugo Alliaume for providing the fix.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/ux-live-component`	≥ 2.8.0&&< 2.36.0	2.36.0`composer require symfony/ux-live-component:^2.36.0`
🐘Packagist	`symfony/ux-live-component`	≥ 3.0.0&&< 3.1.0	3.1.0`composer require symfony/ux-live-component:^3.1.0`

Affected Products

1 product · 2 configurations

Application

uxsymfony

≥ 2.8.0 && < 2.36.0

1 version

3.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/ux-live-component, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/ux-live-component to 2.36.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49212 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Description In `symfony/ux-live-component`, a component's server-side state is exposed to the browser as a set of props (`#[LiveProp]`-annotated properties). Props marked `writable: true` can be freely changed by the client. Read-only props are round-tripped to the browser and back, and their integrity is protected by an HMAC so the client cannot tamper with them. Child components additionally receive a `propsFromParent` blob, also HMAC-signed. The HMAC computed by `Symfony\UX\LiveComponent\LiveComponentHydrator` covered only the sorted prop key/value pairs. It didn't include the compone

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CVE-2026-49212 — ux-live-component

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

Real-World Exposure

Description

Description

Resolution

Credits

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2026-49212 in your dependencies?