// For flags

CVE-2021-47107

NFSD: Fix READDIR buffer overflow

Severity Score

"-"
*CVSS v-

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Fix READDIR buffer overflow

If a client sends a READDIR count argument that is too small (say,
zero), then the buffer size calculation in the new init_dirlist
helper functions results in an underflow, allowing the XDR stream
functions to write beyond the actual buffer.

This calculation has always been suspect. NFSD has never sanity-
checked the READDIR count argument, but the old entry encoders
managed the problem correctly.

With the commits below, entry encoding changed, exposing the
underflow to the pointer arithmetic in xdr_reserve_space().

Modern NFS clients attempt to retrieve as much data as possible
for each READDIR request. Also, we have no unit tests that
exercise the behavior of READDIR at the lower bound of @count
values. Thus this case was missed during testing.

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: NFSD: corrige el desbordamiento del búfer READDIR Si un cliente envía un argumento de recuento READDIR que es demasiado pequeño (digamos, cero), entonces el cálculo del tamaño del búfer en las nuevas funciones auxiliares init_dirlist da como resultado un subdesbordamiento, lo que permite que las funciones de flujo XDR escriban más allá del búfer real. Este cálculo siempre ha sido sospechoso. NFSD nunca ha verificado la cordura del argumento de conteo READDIR, pero los codificadores de entrada antiguos manejaron el problema correctamente. Con las confirmaciones a continuación, la codificación de entrada cambió, exponiendo el desbordamiento a la aritmética del puntero en xdr_reserve_space(). Los clientes NFS modernos intentan recuperar la mayor cantidad de datos posible para cada solicitud READDIR. Además, no tenemos pruebas unitarias que ejerzan el comportamiento de READDIR en el límite inferior de los valores @count. Por lo tanto, este caso se pasó por alto durante las pruebas.

*Credits: N/A
CVSS Scores
Attack Vector
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Attack Complexity
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Privileges Required
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User Interaction
-
Scope
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Confidentiality
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Integrity
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Availability
-
* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-03-04 CVE Reserved
  • 2024-03-04 CVE Published
  • 2024-06-22 EPSS Updated
  • 2024-08-04 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.13 < 5.15.12
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.13 < 5.15.12"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.13 < 5.16
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.13 < 5.16"
en
Affected