high CVSS 7.8

CVE-2021-47131·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: net/tls: Fix use-after-free after the TLS device goes down and up When a netdev with active TLS offload goes down, tls_device_down is called to stop the offload and tear down the TLS context. However, the socket stays alive, and it still points to the TLS context, which is now deallocated. If a netdev goes up, while the connection is still active, and the data flow resumes after a number of TCP retransmissions, it will lead to a use-after-free of the TLS context. This commit addresses this bug by keeping the context alive until its normal destruction, and implements the necessary fallbacks, so that the connection can resume in software (non-offloaded) kTLS mode. On the TX side tls_sw_fallback is used to encrypt all packets. The RX side already has all the necessary fallbacks, because receiving non-decrypted packets is supported. The thing needed on the RX side is to block resync requests, which are normally produced after receiving non-decrypted packets. The necessary synchronization is implemented for a graceful teardown: first the fallbacks are deployed, then the driver resources are released (it used to be possible to have a tls_dev_resync after tls_dev_del). A new flag called TLS_RX_DEV_DEGRADED is added to indicate the fallback mode. It's used to skip the RX resync logic completely, as it becomes useless, and some objects may be released (for example, resync_async, which is allocated and freed by the driver).

Severity: high
Software: Kernel
Fixed in: 5.12.10
Published: 2024-03-15

Affected versions

From: 5.11

Until: 5.12.10

Fixed in: 5.12.10

How to fix this CVE

Update your Linux kernel to version 5.12.10 or later to remediate CVE-2021-47131, which causes memory corruption when TLS offload devices transition offline and back online. This vulnerability can lead to kernel crashes or potential privilege escalation if the freed TLS context is reused. Prioritize this update for systems running kernel versions 5.11 through 5.12.9 that actively use TLS hardware offloading.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

Check your current kernel version: uname -r | grep -E '^5\.(11|12\.[0-9](?!0))' to identify if you are running an affected version between 5.11 and 5.12.9
Verify TLS offload capability is enabled: grep -i tls_device /proc/net/protocols or ethtool -k <interface> | grep tls to see if hardware TLS offloading is active on any network interface
Monitor kernel logs for use-after-free indicators: dmesg | grep -i 'use.after.free\|kasan\|memory corruption\|tls_device' to check for exploitation attempts
Confirm the fix is applied by running uname -r and verifying the version is 5.12.10 or later

FAQ

What is CVE-2021-47131?

CVE-2021-47131 is a use-after-free vulnerability in Linux kernel's TLS device offloading code. When a network device with active TLS offload goes down and then comes back up, the kernel fails to properly manage the TLS context lifecycle, allowing freed memory to be accessed, leading to potential kernel crashes or code execution.

Is CVE-2021-47131 being actively exploited?

No, this vulnerability is not currently listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available. However, the high CVSS score of 7.8 and the local privilege escalation potential warrant timely patching.

What versions of Kernel are affected by CVE-2021-47131?

Linux kernel versions 5.11 through 5.12.9 are affected. The vulnerability was fixed in kernel 5.12.10.

How do I check if my server is vulnerable to CVE-2021-47131?

Run 'uname -r' to check your kernel version. If it shows 5.11.x or 5.12.0 through 5.12.9, your system is vulnerable. Additionally, verify TLS offloading is active with 'ethtool -k <interface> | grep tls' on network interfaces that have devices capable of TLS offloading.

Does Defensia detect CVE-2021-47131?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel package is installed on a monitored server, CVE-2021-47131 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2024-42256CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: cifs: Fix server re-repick on subrequest retry When a subrequest is marked for needing retry, netfs will call cifs_prepare_write() which will make cifs repick the server for the op before renegotiating credits; it then calls cifs_issue_write() which invokes smb2_async_writev() - which re-repicks the server. If a different server is then selected, this causes the increment of server->in_flight to happen against one record and the decrement to happen against another, leading to misaccounting. Fix this by just removing the repick code in smb2_async_writev(). As this is only called from netfslib-driven code, cifs_prepare_write() should always have been called first, and so server should never be NULL and the preparatory step is repeated in the event that we do a retry. The problem manifests as a warning looking something like: WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs] ... RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs] ... smb2_writev_callback+0x334/0x560 [cifs] cifs_demultiplex_thread+0x77a/0x11b0 [cifs] kthread+0x187/0x1d0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30 Which may be triggered by a number of different xfstests running against an Azure server in multichannel mode. generic/249 seems the most repeatable, but generic/215, generic/249 and generic/308 may also show it.

CVE-2024-38541CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: of: module: add buffer overflow check in of_modalias() In of_modalias(), if the buffer happens to be too small even for the 1st snprintf() call, the len parameter will become negative and str parameter (if not NULL initially) will point beyond the buffer's end. Add the buffer overflow check after the 1st snprintf() call and fix such check after the strlen() call (accounting for the terminating NUL char).

CVE-2021-47548CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ethernet: hisilicon: hns: hns_dsaf_misc: fix a possible array overflow in hns_dsaf_ge_srst_by_port() The if statement: if (port >= DSAF_GE_NUM) return; limits the value of port less than DSAF_GE_NUM (i.e., 8). However, if the value of port is 6 or 7, an array overflow could occur: port_rst_off = dsaf_dev->mac_cb[port]->port_rst_off; because the length of dsaf_dev->mac_cb is DSAF_MAX_PORT_NUM (i.e., 6). To fix this possible array overflow, we first check port and if it is greater than or equal to DSAF_MAX_PORT_NUM, the function returns.

CVE-2024-38612CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: sr: fix invalid unregister error path The error path of seg6_init() is wrong in case CONFIG_IPV6_SEG6_LWTUNNEL is not defined. In that case if seg6_hmac_init() fails, the genl_unregister_family() isn't called. This issue exist since commit 46738b1317e1 ("ipv6: sr: add option to control lwtunnel support"), and commit 5559cea2d5aa ("ipv6: sr: fix possible use-after-free and null-ptr-deref") replaced unregister_pernet_subsys() with genl_unregister_family() in this error path.

CVE-2022-48716CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ASoC: codecs: wcd938x: fix incorrect used of portid Mixer controls have the channel id in mixer->reg, which is not same as port id. port id should be derived from chan_info array. So fix this. Without this, its possible that we could corrupt struct wcd938x_sdw_priv by accessing port_map array out of range with channel id instead of port id.

References

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