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CVE-2021-22897: curl 7.61.0 through 7.76.1 suffers from exposure of data element to wrong session due to a mistake in the c...

curl 7.61.0 through 7.76.1 suffers from exposure of data element to wrong session due to a mistake in the code for CURLOPT_SSL_CIPHER_LIST when libcurl is built to use the Schannel TLS library. The selected cipher set was stored in a single "static" variable in the library, which has the surprising side-effect that if an application sets up multiple concurrent transfers, the last one that sets the ciphers will accidentally control the set used by all transfers. In a worst-case scenario, this weakens transport security significantly.

MediumCVSS 5.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This curl/libcurl issue can make one transfer's TLS cipher preference unintentionally affect other concurrent transfers. The main business risk is weakened transport security for applications using affected libcurl versions with the Windows Schannel TLS backend. It is not listed in KEV, and the provided sources do not show active exploitation.

Executive priority

Treat this as a targeted hygiene fix, not an emergency. Prioritize internet-facing or sensitive-data systems using affected Windows Schannel libcurl builds, especially embedded vendor products. Remediate through normal patch cycles unless local inventory confirms high-value concurrent transfer workloads.

Technical view

In curl 7.61.0 through 7.76.1, CURLOPT_SSL_CIPHER_LIST state was stored in a static variable when libcurl used Schannel. Concurrent transfers could therefore share the last configured cipher list, causing the wrong session to use an unintended cipher set. CVSS 3.1 is 5.3, confidentiality impact low, with no integrity or availability impact scored.

Likely exposure

Exposure is most likely in Windows applications or products embedding libcurl 7.61.0 through 7.76.1, built with Schannel, using CURLOPT_SSL_CIPHER_LIST, and running concurrent transfers. Downstream products may be affected through bundled curl, as reflected by vendor advisories from Oracle, NetApp, and Siemens.

Exploitation context

The source bundle marks KEV as false and provides no cited evidence of active exploitation. The weakness requires a specific runtime pattern: affected Schannel-backed libcurl, customized cipher lists, and concurrent transfers. The impact is transport security weakening rather than direct code execution or service outage.

Researcher notes

The key exposure discriminator is not just curl version; it is Schannel plus CURLOPT_SSL_CIPHER_LIST plus concurrency. Evidence in the bundle supports confidentiality risk through unintended cipher selection. It does not support claims of active exploitation, broad remote compromise, or impact outside the affected backend and versions.

Mitigation direction

  • Upgrade curl/libcurl to a non-affected release per curl guidance.
  • Apply downstream vendor updates for products embedding affected curl versions.
  • Prioritize Windows Schannel deployments using custom cipher lists and concurrent transfers.
  • Review Oracle, NetApp, and Siemens advisories for product-specific remediation.
  • If immediate upgrade is unavailable, ask the vendor for supported compensating controls.

Validation and detection

  • Inventory curl and libcurl versions across servers, appliances, and packaged products.
  • Confirm whether libcurl is built with the Schannel TLS backend.
  • Identify applications setting CURLOPT_SSL_CIPHER_LIST during concurrent transfers.
  • Check vendor advisories for embedded curl exposure and fixed releases.
  • Validate that updated builds isolate cipher configuration per transfer.
Prepared
Confidence
high
Sources
10

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-2021-22897 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.3 (3.1)
Known Exploited
No
Published

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

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
9Source 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
5.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N3.91.4CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

5.3Medium
CVSS 3.1 vector shape for CVE-2021-22897Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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/curl7.61.0 through 7.76.1Listed
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

Business Logic Errors represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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