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CVE Record

CVE-2021-22926: libcurl-using applications can ask for a specific client certificate to be used in a transfer.

libcurl-using applications can ask for a specific client certificate to be used in a transfer. This is done with the `CURLOPT_SSLCERT` option (`--cert` with the command line tool).When libcurl is built to use the macOS native TLS library Secure Transport, an application can ask for the client certificate by name or with a file name - using the same option. If the name exists as a file, it will be used instead of by name.If the appliction runs with a current working directory that is writable by other users (like `/tmp`), a malicious user can create a file name with the same name as the app wants to use by name, and thereby trick the application to use the file based cert instead of the one referred to by name making libcurl send the wrong client certificate in the TLS connection handshake.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This affects libcurl applications on macOS when libcurl uses Secure Transport and selects a client certificate by name. If the application runs from a directory other users can write to, another local user can influence which certificate is sent. This can break trust assumptions for certificate-based authentication.

Executive priority

Prioritize remediation where certificate-based authentication protects sensitive systems. The issue is not broadly internet-exploitable from the supplied evidence, but affected enterprise products and client-certificate workflows can create meaningful trust and availability risk.

Technical view

In curl/libcurl 7.33.0 through 7.77.0, CURLOPT_SSLCERT can resolve a requested certificate name as a local filename first under Secure Transport. In a writable current working directory, a matching file can cause libcurl to use a file-based certificate instead of the intended named certificate.

Likely exposure

Exposure is narrow but important: macOS-hosted applications or bundled products using affected libcurl, Secure Transport, client certificate authentication, and a current working directory writable by other users.

Exploitation context

The CVE source describes a local file-placement condition, not remote unauthenticated exploitation. KEV is false, and the provided sources do not show active exploitation in the wild.

Researcher notes

Focus on the exact preconditions: libcurl 7.33.0-7.77.0, macOS Secure Transport, certificate selection by name, and writable current working directory. Do not generalize this to all curl deployments or all TLS backends without vendor evidence.

Mitigation direction

  • Upgrade curl/libcurl outside the affected 7.33.0 through 7.77.0 range where vendor guidance supports it.
  • Check OS, appliance, and application vendor advisories for packaged libcurl fixes.
  • Do not run affected libcurl clients from directories writable by untrusted users.
  • Review uses of CURLOPT_SSLCERT or curl --cert on macOS Secure Transport builds.

Validation and detection

  • Inventory curl/libcurl versions embedded in macOS applications and third-party products.
  • Confirm whether libcurl is built with Secure Transport rather than another TLS backend.
  • Identify workflows using client certificate names with CURLOPT_SSLCERT or curl --cert.
  • Check service working directories for world-writable or shared-write permissions.
  • Review vendor advisories for Oracle, NetApp, Siemens, Gentoo, and affected application stacks.
Prepared
Confidence
medium
Sources
9

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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cwe · low confidence lookup

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cve · low confidence lookup

CVE-2021-22926 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
2ADP providers
12Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: pocAutomatable: yesTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2021-22926Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/ahttps://github.com/curl/curlcurll 7.33.0 to and include 7.77.0Listed
Weakness

CWE details

CWE-840

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-840 · source CWE mapping

Business Logic Errors

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