Evidence used
- No CISA KEV confirmation is currently recorded.
- A structured source references public exploit or proof-of-concept material.
- EPSS is 0.92% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2021
CVE-2021-32825High confidence
ZipSlip vulnerability in bblfshd
bblfsh · bblfshd
2.7LowCVSS 3.1
Within 7 days
Patch availableLow technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityLow→Operational priority:Low, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict local access and enforce least privilege on affected hosts.
- Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
- Confirm that the asset runs bblfsh bblfshd 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.
Low technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.
Patch available01
What, why and how
bblfshd is an open source self-hosted server for source code parsing. In bblfshd before commit 4265465b9b6fb5663c30ee43806126012066aad4 there is a "zipslip" vulnerability. The unsafe handling of symbolic links in an unpacking routine may enable attackers to read and/or write to arbitrary locations outside the designated target folder. This issue may lead to arbitrary file write (with same permissions as the program running the unpack operation) if the attacker can control the archive file. Additionally, if the attacker has read access to the unpacked files, he may be able to read arbitrary system files the parent process has permissions to read. For more details including a PoC see the referenced GHSL-2020-258.
What
bblfshd is an open source self-hosted server for source code parsing. In bblfshd before commit 4265465b9b6fb5663c30ee43806126012066aad4 there is a "zipslip" vulnerability. The unsafe handling of symbolic links in an unpacking routine may enable attackers to read and/or write to arbitrary locations outside the designated target folder. This issue may lead to arbitrary file write (with same permissions as the program running the unpack operation) if the attacker can control the archive file. Additionally, if the attacker has read access to the unpacked files, he may be able to read arbitrary system files the parent process has permissions to read. For more details including a PoC see the referenced GHSL-2020-258.
Why
The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as .. that can resolve to a location that is outside of that directory.
How
An attacker operating through local access may attempt exploitation without authentication after a user interaction. If successful, the issue may obtain information outside the intended access boundary.
What
bblfshd is an open source self-hosted server for source code parsing. In bblfshd before commit 4265465b9b6fb5663c30ee43806126012066aad4 there is a "zipslip" vulnerability. The unsafe handling of symbolic links in an unpacking routine may enable attackers to read and/or write to arbitrary locations outside the designated target folder. This issue may lead to arbitrary file write (with same permissions as the program running the unpack operation) if the attacker can control the archive file. Additionally, if the attacker has read access to the unpacked files, he may be able to read arbitrary system files the parent process has permissions to read. For more details including a PoC see the referenced GHSL-2020-258.
Why
The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as .. that can resolve to a location that is outside of that directory.
How
An attacker operating through local access may attempt exploitation without authentication after a user interaction. If successful, the issue may obtain information outside the intended access boundary.
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 Reference recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.
- Likely attack path
- local access → Relative Path Traversal → obtain information outside the intended access boundary
- Attack surface
- Local
- Privileges required
- None: unauthenticated exploitation is possible
- User interaction
- Required interaction required
- Attack complexity
- High: exploitation depends on specific conditions
- Security boundary
- Changed: exploitation can affect a different security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-23 ↗
CWE-23: Relative Path Traversal. The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as .. that can resolve to a location that is outside of that directory.
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:C/C:L/I:N/A:NCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SChangedScope: The attack can affect a component governed by a different security 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
- The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
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. Limit untrusted access and use least privilege until authoritative guidance is available.
04
Evidence and provenance
Published 16 Aug 2021 · Last source change 3 Aug 2024, 23:33 UTC · CWE-23 · Relative Path Traversal
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-2021-19567
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.