VulnerabilityPublished 29 Apr 2026Updated 23 Sep 2026

CVE-2026-5773: some circumstances reuse the wrong connection · Libcurl Might

Affects curlSource GCVE Database

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Not known to be exploited · CVSS 7.5 High · fixed in 7.47.0-1ubuntu2.19+esm17 : patch curl soon.

Data as of 7 Nov 2026, 23:24 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.6% chance of exploitation in 30 days – higher than 49% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 7.47.0-1ubuntu2.19+esm17, 7.58.0-2ubuntu3.24+esm10, 7.68.0-1ubuntu2.25+esm5 +4

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 29 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 8 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Patches and advisories

Affected software

Product	Affected	Fixed in
Ubuntu 26.04 LTScurl`pkg:deb/ubuntu/curl?arch=source&distro=resolute`Other threats	Affected <8.18.0-1ubuntu2.1	Fixed in 8.18.0-1ubuntu2.1
Ubuntu 25.10curl`pkg:deb/ubuntu/curl?arch=source&distro=questing`Other threats	Affected <8.14.1-2ubuntu1.3	Fixed in 8.14.1-2ubuntu1.3
Ubuntu 24.04 LTScurl`pkg:deb/ubuntu/curl?arch=source&distro=noble`Other threats	Affected <8.5.0-2ubuntu10.9	Fixed in 8.5.0-2ubuntu10.9
Ubuntu 22.04 LTScurl`pkg:deb/ubuntu/curl?arch=source&distro=jammy`Other threats	Affected <7.81.0-1ubuntu1.24	Fixed in 7.81.0-1ubuntu1.24
Ubuntu Pro 20.04 LTScurl`pkg:deb/ubuntu/curl?arch=source&distro=esm-infra/focal`Other threats	Affected <7.68.0-1ubuntu2.25+esm5	Fixed in 7.68.0-1ubuntu2.25+esm5
Ubuntu Pro 18.04 LTScurl`pkg:deb/ubuntu/curl?arch=source&distro=esm-infra/bionic`Other threats	Affected <7.58.0-2ubuntu3.24+esm10	Fixed in 7.58.0-2ubuntu3.24+esm10

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Official patches are available from Ubuntu for affected curl packages. Users should update to the fixed versions as listed in Ubuntu security notices USN-8227-1 and USN-8525-1. Applying these updates will correct the connection reuse logic and prevent the vulnerability. Standard system updates or Ubuntu Pro subscription updates will include these fixes.

Description

A logical error in libcurl's connection reuse logic for SMB(S) transfers can cause the reuse of an existing SMB connection to the same server but with a different share than intended. This may lead to downloading the wrong file or uploading a file to an incorrect location while using the same credentials and server name. The issue affects multiple Ubuntu package versions of curl and has a CVSS score of 7.5. Official patches are available from Ubuntu to address this vulnerability.

Impact

An attacker or application could cause libcurl to reuse an SMB connection tied to a different share than intended, potentially leading to unauthorized file downloads or uploads on the SMB server. The confidentiality of data may be compromised due to exposure of unintended files. The vulnerability does not affect integrity or availability. The issue is limited to SMB(S) transfers using libcurl's connection reuse feature.

Summary

libcurl maintains a pool of recent connections to optimize network transfers by reusing existing connections when possible. Due to a logical flaw, libcurl may incorrectly reuse an SMB connection associated with a different share than the one required for a new transfer. This can cause file operations to be performed on unintended shares, potentially resulting in the download or upload of incorrect files. The vulnerability affects several Ubuntu curl package versions prior to patched releases. The issue is tracked as CVE-2026-5773 with a CVSS 3.1 score of 7.5 (network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, high confidentiality impact, no integrity or availability impact).

References

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