Evidence used
- No CISA KEV confirmation is currently recorded.
- The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
- EPSS is 1.71% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2021
CVE-2021-21424High confidence
Prevent user enumeration using Guard or the new Authenticator-based Security
symfony · symfony
Official source article: GitHub GHSA-5PV8-PPVJ-4H68 ↗. Check the applicable product and release in the original source.
5.3MediumCVSS 3.1
Scheduled
Patch availableMedium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityMedium→Operational priority:Medium, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs symfony symfony and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Distribution package intelligence
4 package statesRelease-specific package status
Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
| Distribution release | Source package | Vendor state | Fixed version | Evidence |
|---|---|---|---|---|
| Debian trixietrixie · source | symfony | Vendor fix publishedDebian records a fixed source-package version for this release. | 4.4.19+dfsg-2 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian bookwormbookworm · source | symfony | Vendor fix publishedDebian records a fixed source-package version for this release. | 4.4.19+dfsg-2 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian forkyforky · source | symfony | Vendor fix publishedDebian records a fixed source-package version for this release. | 4.4.19+dfsg-2 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian sidsid · source | symfony | Vendor fix publishedDebian records a fixed source-package version for this release. | 4.4.19+dfsg-2 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
Open-source package ranges17 source-attributed ranges
These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.
| Ecosystem and package | Affected range | First fixed version | Evidence |
|---|---|---|---|
| Packagistlexik/jwt-authentication-bundle | ECOSYSTEM: introduced 2.0.0; fixed 2.10.7 | 2.10.7 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistlexik/jwt-authentication-bundle | ECOSYSTEM: introduced 2.11.0; fixed 2.11.3 | 2.11.3 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/maker-bundle | ECOSYSTEM: introduced 1.27.0; fixed 1.29.2 | 1.29.2 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/maker-bundle | ECOSYSTEM: introduced 1.30.0; fixed 1.31.1 | 1.31.1 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security | ECOSYSTEM: introduced 5.0.0; fixed 5.2.8 | 5.2.8 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security | ECOSYSTEM: introduced 2.8.0; fixed 3.4.49 | 3.4.49 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security | ECOSYSTEM: introduced 4.0.0; fixed 4.4.24 | 4.4.24 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-core | ECOSYSTEM: introduced 2.8.0; fixed 3.4.48 | 3.4.48 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-core | ECOSYSTEM: introduced 4.0.0; fixed 4.4.23 | 4.4.23 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-core | ECOSYSTEM: introduced 5.0.0; fixed 5.2.8 | 5.2.8 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-guard | ECOSYSTEM: introduced 2.8.0; fixed 3.4.48 | 3.4.48 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-guard | ECOSYSTEM: introduced 4.0.0; fixed 4.4.23 | 4.4.23 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-guard | ECOSYSTEM: introduced 5.0.0; fixed 5.2.8 | 5.2.8 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/security-http | ECOSYSTEM: introduced 5.1.0; fixed 5.2.8 | 5.2.8 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/symfony | ECOSYSTEM: introduced 2.8.0; fixed 3.4.49 | 3.4.49 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/symfony | ECOSYSTEM: introduced 4.0.0; fixed 4.4.24 | 4.4.24 | OSV record ↗aggregator derived · 10 Sep 2026 |
| Packagistsymfony/symfony | ECOSYSTEM: introduced 5.0.0; fixed 5.2.9 | 5.2.9 | OSV record ↗aggregator derived · 10 Sep 2026 |
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.
Patch available01
What, why and how
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. The ability to enumerate users was possible without relevant permissions due to different handling depending on whether the user existed or not when attempting to use the switch users functionality. We now ensure that 403s are returned whether the user exists or not if a user cannot switch to a user or if the user does not exist. The patch for this issue is available for branch 3.4.
What
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. The ability to enumerate users was possible without relevant permissions due to different handling depending on whether the user existed or not when attempting to use the switch users functionality. We now ensure that 403s are returned whether the user exists or not if a user cannot switch to a user or if the user does not exist. The patch for this issue is available for branch 3.4.
Why
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
What
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. The ability to enumerate users was possible without relevant permissions due to different handling depending on whether the user existed or not when attempting to use the switch users functionality. We now ensure that 403s are returned whether the user exists or not if a user cannot switch to a user or if the user does not exist. The patch for this issue is available for branch 3.4.
Why
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → Exposure of Sensitive Information to an Unauthorized Actor → cause the confidentiality, integrity or availability impact described by the vendor
- Attack surface
- Network
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- None
- Attack complexity
- Low: no specialised conditions are recorded
- Security boundary
- Unchanged: impact remains within the vulnerable component's security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-200 ↗
CWE-200: Exposure of Sensitive Information to an Unauthorized Actor. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:NCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CLowConfidentiality impact: A successful attack can cause a limited loss.INoneIntegrity impact: No direct loss is represented by this metric.ANoneAvailability impact: No direct loss is represented by this metric.- Post-exploitation / living off the land
- No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Patch available
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 13 May 2021 · Last source change 3 Aug 2024, 18:09 UTC · CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor
CVE recordCVE.org · 5.1
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2021-0960
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD modified after enrichment
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.
CVE published
Fixed release or patch reference recorded
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.