NCSC-2026-0210

Vulnerability from csaf_ncscnl - Published: 2026-06-23 09:53 - Updated: 2026-06-24 09:01
Summary
Kwetsbaarheden verholpen in libssh2 door libssh
Notes
The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this page to enhance access to its information and security advisories. The use of this security advisory is subject to the following terms and conditions: NCSC-NL makes every reasonable effort to ensure that the content of this page is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or continuous keeping up-to-date. The information contained in this security advisory is intended solely for the purpose of providing general information to professional users. No rights can be derived from the information provided therein. NCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of this security advisory. This includes damage resulting from the inaccuracy of incompleteness of the information contained in the advisory. This security advisory is subject to Dutch law. All disputes related to or arising from the use of this advisory will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings.
Feiten: libssh heeft kwetsbaarheden verholpen in libssh2 tot en met versie 1.11.1.
Interpretaties: De eerste kwetsbaarheid betreft een pre-authenticatie denial of service in de SSH_MSG_EXT_INFO handler. Een kwaadaardige SSH-server kan een speciaal geconstrueerde extension_count waarde sturen, waardoor de client in een CPU-uitputtingslus terechtkomt en de verwerking van SSH-berichten verstoord wordt. De tweede kwetsbaarheid zit in de ssh2_transport_read() functie, waar onjuiste bounds checking op de packet_length variabele leidt tot een out-of-bounds write. Dit kan door een aanvaller worden misbruikt om met speciaal geconstrueerde SSH-pakketten een Denial-of-Service te veroorzaken, of in theorie om willekeurige code uit te voeren op het getroffen systeem, indien er geen additionele maatregelen zijn genomen als Address Space Layout Randomization (ALSR). Dit is echter geen gebruikelijke instelling op systemen. Beide kwetsbaarheden zijn aanwezig in alle implementaties die libssh2 versie 1.11.1 of lager gebruiken. Update: Er is publieke PoC code verschenen die bevestigd dat de kwetsbaarheid onder specifieke mogelijkheden kan leiden tot het uitvoeren van willekeurige code.
Oplossingen: libssh heeft updates uitgebracht om de kwetsbaarheden te verhelpen. Zie bijgevoegde referenties voor meer informatie.
Kans: medium
Schade: high
CWE-680: Integer Overflow to Buffer Overflow
CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
CVE-2026-55199

libssh2 versions through 1.11.1 contain a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler that allows a malicious SSH server to cause client CPU exhaustion via a crafted extension count, fixed in commit 1762685.

5.9 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE-835 - Loop with Unreachable Exit Condition ('Infinite Loop')
Affected products
Product Identifier Version Remediation
vers:unknown/*
Open Source / libssh2
 vers:unknown/*
vers:unknown/*
libssh2 / libssh2
 vers:unknown/*
CVE-2026-55200

libssh2 versions up to 1.11.1 contain an out-of-bounds write vulnerability in ssh2_transport_read() due to improper bounds checking on packet_length, enabling remote attackers to execute arbitrary code via crafted SSH packets.

8.1 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Affected products
Known affected 2 products, the same list as for CVE-2026-55199
References
To clipboard 

{
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    "distribution": {
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    "notes": [
      {
        "category": "legal_disclaimer",
        "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this page to enhance access to its information and security advisories. The use of this security advisory is subject to the following terms and conditions:\n\n    NCSC-NL makes every reasonable effort to ensure that the content of this page is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or continuous keeping up-to-date. The information contained in this security advisory is intended solely for the purpose of providing general information to professional users. No rights can be derived from the information provided therein.\n\n    NCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of this security advisory. This includes damage resulting from the inaccuracy of incompleteness of the information contained in the advisory.\n    This security advisory is subject to Dutch law. All disputes related to or arising from the use of this advisory will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings."
      },
      {
        "category": "description",
        "text": "libssh heeft kwetsbaarheden verholpen in libssh2 tot en met versie 1.11.1.",
        "title": "Feiten"
      },
      {
        "category": "description",
        "text": "De eerste kwetsbaarheid betreft een pre-authenticatie denial of service in de SSH_MSG_EXT_INFO handler. Een kwaadaardige SSH-server kan een speciaal geconstrueerde extension_count waarde sturen, waardoor de client in een CPU-uitputtingslus terechtkomt en de verwerking van SSH-berichten verstoord wordt. De tweede kwetsbaarheid zit in de ssh2_transport_read() functie, waar onjuiste bounds checking op de packet_length variabele leidt tot een out-of-bounds write. Dit kan door een aanvaller worden misbruikt om met speciaal geconstrueerde SSH-pakketten een Denial-of-Service te veroorzaken, of in theorie om willekeurige code uit te voeren op het getroffen systeem, indien er geen additionele maatregelen zijn genomen als Address Space Layout Randomization (ALSR). Dit is echter geen gebruikelijke instelling op systemen. Beide kwetsbaarheden zijn aanwezig in alle implementaties die libssh2 versie 1.11.1 of lager gebruiken.\n\nUpdate: Er is publieke PoC code verschenen die bevestigd dat de kwetsbaarheid onder specifieke mogelijkheden kan leiden tot het uitvoeren van willekeurige code.",
        "title": "Interpretaties"
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        "title": "CWE-680"
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        "url": "https://github.com/advisories/GHSA-3CFQ-4XX4-RMPG"
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        "summary": "Reference",
        "url": "https://github.com/advisories/GHSA-R8MH-X5QV-7GG2"
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    "title": "Kwetsbaarheden verholpen in libssh2 door libssh",
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          "title": "Summary"
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        {
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}



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